<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e2887-1238-742d-bd2a-ee91c80ab2b9,g:98de0316-52d2-4da0-b4d3-bc7a085beb53-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.americanassets.com/role/CoverPage" xlink:type="simple" xlink:href="aat-20260630.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019e2887-1480-7e93-b3dd-80d40abb522e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntitiesTable_019e2887-1480-7e93-b3dd-80d40abb522e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-71c2-b80a-175c7db28cf7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019e2887-1480-7e93-b3dd-80d40abb522e" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-71c2-b80a-175c7db28cf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-71c2-b80a-175c7db28cf7_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-71c2-b80a-175c7db28cf7" xlink:to="loc_dei_EntityDomain_019e2887-1480-71c2-b80a-175c7db28cf7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7512-89f8-692d23158a95" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-71c2-b80a-175c7db28cf7" xlink:to="loc_dei_EntityDomain_019e2887-1480-7512-89f8-692d23158a95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7cf9-bcc2-9ac069c2cb68" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-7512-89f8-692d23158a95" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7cf9-bcc2-9ac069c2cb68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e2887-1480-7f56-a0a3-64cc693c67a0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentType_019e2887-1480-7f56-a0a3-64cc693c67a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019e2887-1480-71f0-8f27-7ae477121ab5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentQuarterlyReport_019e2887-1480-71f0-8f27-7ae477121ab5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019e2887-1480-715a-bfd8-000915c7d62d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentPeriodEndDate_019e2887-1480-715a-bfd8-000915c7d62d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019e2887-1480-740d-bef7-96238eeb82f0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentTransitionReport_019e2887-1480-740d-bef7-96238eeb82f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e2887-1480-705b-9e42-a17dedd56e05" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityRegistrantName_019e2887-1480-705b-9e42-a17dedd56e05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019e2887-1480-7217-bb38-888100c6a1c1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityFileNumber_019e2887-1480-7217-bb38-888100c6a1c1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019e2887-1480-7e14-80db-17f0f8b8803f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019e2887-1480-7e14-80db-17f0f8b8803f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e2887-1480-7345-8604-7404db3e2402" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e2887-1480-7345-8604-7404db3e2402" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019e2887-1480-787d-ba95-1e5e5d83f791" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityAddressAddressLine1_019e2887-1480-787d-ba95-1e5e5d83f791" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019e2887-1480-7d84-9a29-86672287edce" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityAddressAddressLine2_019e2887-1480-7d84-9a29-86672287edce" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019e2887-1480-7d0d-a1b8-3e3fb6ce02be" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityAddressCityOrTown_019e2887-1480-7d0d-a1b8-3e3fb6ce02be" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019e2887-1480-761c-bdab-dac3b339b072" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityAddressStateOrProvince_019e2887-1480-761c-bdab-dac3b339b072" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019e2887-1480-7b95-8db6-4b09d450254d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityAddressPostalZipCode_019e2887-1480-7b95-8db6-4b09d450254d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019e2887-1480-7356-8346-a3adf9750e56" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_CityAreaCode_019e2887-1480-7356-8346-a3adf9750e56" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019e2887-1480-7c1a-a472-2bddaa451cc9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_LocalPhoneNumber_019e2887-1480-7c1a-a472-2bddaa451cc9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019e2887-1480-766c-a143-ade223324963" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityCurrentReportingStatus_019e2887-1480-766c-a143-ade223324963" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019e2887-1480-76cb-b068-c43c9df457ed" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityInteractiveDataCurrent_019e2887-1480-76cb-b068-c43c9df457ed" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019e2887-1480-77a2-80f8-352d74fab154" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityFilerCategory_019e2887-1480-77a2-80f8-352d74fab154" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019e2887-1480-7876-b026-a134a57fe7d3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntitySmallBusiness_019e2887-1480-7876-b026-a134a57fe7d3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019e2887-1480-7b18-a3c9-5eff32c81481" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityEmergingGrowthCompany_019e2887-1480-7b18-a3c9-5eff32c81481" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019e2887-1480-7195-8bfb-3bdf3eb78e12" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityShellCompany_019e2887-1480-7195-8bfb-3bdf3eb78e12" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019e2887-1480-740b-89c5-ef54fc1677a5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_Security12bTitle_019e2887-1480-740b-89c5-ef54fc1677a5" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019e2887-1480-7a8a-970c-6bfeb8b91eeb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_TradingSymbol_019e2887-1480-7a8a-970c-6bfeb8b91eeb" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019e2887-1480-714f-8df6-2d71e91b6c8c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_SecurityExchangeName_019e2887-1480-714f-8df6-2d71e91b6c8c" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019e2887-1480-7fa6-9d13-d6343a10bc40" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019e2887-1480-7fa6-9d13-d6343a10bc40" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e2887-1480-7ea9-9103-965f0598f42c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_AmendmentFlag_019e2887-1480-7ea9-9103-965f0598f42c" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019e2887-1480-73b0-a57c-3ebe4480eebf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentFiscalYearFocus_019e2887-1480-73b0-a57c-3ebe4480eebf" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019e2887-1480-79c2-b7a4-5e6973d4e30d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019e2887-1480-79c2-b7a4-5e6973d4e30d" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e2887-1480-74cb-b5b4-3202f109e5d0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_EntityCentralIndexKey_019e2887-1480-74cb-b5b4-3202f109e5d0" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019e2887-1480-7336-a01e-d2ffafb76948" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019e2887-1480-7d32-b39d-aacf1f76f17a" xlink:to="loc_dei_CurrentFiscalYearEndDate_019e2887-1480-7336-a01e-d2ffafb76948" xlink:type="arc" order="29"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedStatementofEquity" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedStatementofEquity"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedStatementofEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-7420-8860-8410fc035e5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-79be-970b-46a260880bda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7420-8860-8410fc035e5b" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-79be-970b-46a260880bda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e2887-1480-7478-8d41-1d05896d22f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-79be-970b-46a260880bda" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e2887-1480-7478-8d41-1d05896d22f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2887-1480-7478-8d41-1d05896d22f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e2887-1480-7478-8d41-1d05896d22f7" xlink:to="loc_us-gaap_EquityComponentDomain_019e2887-1480-7478-8d41-1d05896d22f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e2887-1480-7478-8d41-1d05896d22f7" xlink:to="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e2887-1480-71a7-ad8c-74fc38c1ebc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:to="loc_us-gaap_CommonStockMember_019e2887-1480-71a7-ad8c-74fc38c1ebc9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e2887-1480-7b73-a790-4e7e13654194" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e2887-1480-7b73-a790-4e7e13654194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e2887-1480-73b3-865a-29cbc8be3137" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:to="loc_us-gaap_RetainedEarningsMember_019e2887-1480-73b3-865a-29cbc8be3137" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2887-1480-799f-a4ac-e0d99c3a8903" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2887-1480-799f-a4ac-e0d99c3a8903" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019e2887-1480-7fc5-bf9e-12ca6ba5691b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-1480-7a86-bf5e-c72896daf2a5" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019e2887-1480-7fc5-bf9e-12ca6ba5691b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7420-8860-8410fc035e5b" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e2887-1480-7d4a-b4ad-adccc408f260" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e2887-1480-7d4a-b4ad-adccc408f260" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019e2887-1480-755f-b55f-3037462d8d20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019e2887-1480-755f-b55f-3037462d8d20" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019e2887-1480-718e-af66-849f259db815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_ProfitLoss_019e2887-1480-718e-af66-849f259db815" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019e40ad-ba4d-7250-9b3e-15836c965470" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019e40ad-ba4d-7250-9b3e-15836c965470" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_019e3fc7-eede-7814-a85e-c8249d026ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_019e3fc7-eede-7814-a85e-c8249d026ff9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019e2887-1480-7edb-9645-2987141ba4b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019e2887-1480-7edb-9645-2987141ba4b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019e2887-1480-70fa-8426-c018fd9e06fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019e2887-1480-70fa-8426-c018fd9e06fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e2887-1480-7b9b-b6eb-17417a7a6796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e2887-1480-7b9b-b6eb-17417a7a6796" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-7d94-9ec3-b4c083581cb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-7d94-9ec3-b4c083581cb7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-7a27-bc58-fb727d0d1762" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2887-1480-7069-8a92-b68d644b482f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-7a27-bc58-fb727d0d1762" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e2887-1480-765c-a57c-8296aa4f376c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019e2887-1480-7103-bef4-ed44c4aa9241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedBalanceSheetsLP" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedBalanceSheetsLP"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedBalanceSheetsLP" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-7781-9fe0-9dc92e222886" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-7d22-93bc-ef0dc3962f10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7781-9fe0-9dc92e222886" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-7d22-93bc-ef0dc3962f10" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-75f8-968d-86e02f5a69e3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7d22-93bc-ef0dc3962f10" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-75f8-968d-86e02f5a69e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-75f8-968d-86e02f5a69e3_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-75f8-968d-86e02f5a69e3" xlink:to="loc_dei_EntityDomain_019e2887-1480-75f8-968d-86e02f5a69e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7f0c-bc4e-2c2cb761629f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-75f8-968d-86e02f5a69e3" xlink:to="loc_dei_EntityDomain_019e2887-1480-7f0c-bc4e-2c2cb761629f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7172-a3aa-856568b10274" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-7f0c-bc4e-2c2cb761629f" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7172-a3aa-856568b10274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7781-9fe0-9dc92e222886" xlink:to="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RentalProperties_019e2887-1480-75e7-90a3-09c9495bcfed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RentalProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_RentalProperties_019e2887-1480-75e7-90a3-09c9495bcfed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressGross_019e2887-1480-7ef3-b8b2-6d10e32ace11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_ConstructionInProgressGross_019e2887-1480-7ef3-b8b2-6d10e32ace11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAvailableForDevelopment_019e2887-1480-7ebc-9e25-47fac23b8411" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAvailableForDevelopment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_LandAvailableForDevelopment_019e2887-1480-7ebc-9e25-47fac23b8411" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAtCost_019e2887-1480-7100-85d7-46f3eed700b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAtCost_019e2887-1480-7100-85d7-46f3eed700b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_019e2887-1480-7dbc-ae4f-dbce103f8c71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_019e2887-1480-7dbc-ae4f-dbce103f8c71" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNet_019e2887-1480-7b51-95c9-47959aa639a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_019e2887-1480-7273-a2b7-d53e8366e6e2" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNet_019e2887-1480-7b51-95c9-47959aa639a1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e2887-1480-7920-ba8b-fad058cd4472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e2887-1480-7920-ba8b-fad058cd4472" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNet_019e2887-1480-7715-af02-26eced9f5dad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_AccountsReceivableNet_019e2887-1480-7715-af02-26eced9f5dad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRentReceivablesNet_019e2887-1480-7cac-8c21-4ffaf5402b88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRentReceivablesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_DeferredRentReceivablesNet_019e2887-1480-7cac-8c21-4ffaf5402b88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_019e2887-1480-70c6-acd1-84803c7876ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_OtherAssets_019e2887-1480-70c6-acd1-84803c7876ae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019e2887-1480-7afd-8098-32510b8c8152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e2887-1480-762d-bc52-6d8981dbfec5" xlink:to="loc_us-gaap_Assets_019e2887-1480-7afd-8098-32510b8c8152" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7781-9fe0-9dc92e222886" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:to="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebt_019e2887-1480-703c-9170-8e0aa56ed02b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_SecuredDebt_019e2887-1480-703c-9170-8e0aa56ed02b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebt_019e2887-1480-711a-b319-4d0ba5616267" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_UnsecuredDebt_019e2887-1480-711a-b319-4d0ba5616267" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent_019e2887-1480-76bc-8b78-9767b9930b4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent_019e2887-1480-76bc-8b78-9767b9930b4c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecurityDepositLiability_019e2887-1480-7977-b623-4bbf02ba6e76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecurityDepositLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_SecurityDepositLiability_019e2887-1480-7977-b623-4bbf02ba6e76" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCreditsAndOtherLiabilities_019e2887-1480-731e-a596-cce1ca14a2bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCreditsAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_DeferredCreditsAndOtherLiabilities_019e2887-1480-731e-a596-cce1ca14a2bd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019e2887-1480-7b46-a103-9a1840433e27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019e2887-1480-73ba-8c72-f79632f68f05" xlink:to="loc_us-gaap_Liabilities_019e2887-1480-7b46-a103-9a1840433e27" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019e2887-1480-7e4a-9637-415b15ca5886" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019e2887-1480-7e4a-9637-415b15ca5886" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:to="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccount_019e2887-1480-7c4c-9911-07ba2cf69c1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnersCapitalAccount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:to="loc_us-gaap_LimitedPartnersCapitalAccount_019e2887-1480-7c4c-9911-07ba2cf69c1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnersCapitalAccount_019e2887-1480-7144-b5a7-686193cd75ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnersCapitalAccount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:to="loc_us-gaap_GeneralPartnersCapitalAccount_019e2887-1480-7144-b5a7-686193cd75ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019e2887-1480-7506-a453-ef30eb4862ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019e2887-1480-7506-a453-ef30eb4862ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapital_019e2887-1480-7ef8-a408-194b28046583" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnersCapitalAbstract_019e2887-1480-701b-9710-051050193706" xlink:to="loc_us-gaap_PartnersCapital_019e2887-1480-7ef8-a408-194b28046583" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019e2887-1480-7ff8-9a78-dc172edcadee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e2887-1480-7833-a359-48a16e737c34" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019e2887-1480-7ff8-9a78-dc172edcadee" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedBalanceSheetsLPParenthetical" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedBalanceSheetsLPParenthetical"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedBalanceSheetsLPParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-7452-bb83-32acdaa67ff2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-7452-bb83-32acdaa67ff2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-7dd0-b2d2-0e9a20b08f45" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7452-bb83-32acdaa67ff2" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-7dd0-b2d2-0e9a20b08f45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7dd0-b2d2-0e9a20b08f45_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-7dd0-b2d2-0e9a20b08f45" xlink:to="loc_dei_EntityDomain_019e2887-1480-7dd0-b2d2-0e9a20b08f45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7d90-a6e3-c4db7943ef9a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-7dd0-b2d2-0e9a20b08f45" xlink:to="loc_dei_EntityDomain_019e2887-1480-7d90-a6e3-c4db7943ef9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7066-958a-65d07237766b" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-7d90-a6e3-c4db7943ef9a" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7066-958a-65d07237766b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccountUnitsIssued_019e2887-1480-74e0-99b2-b70654fab4fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnersCapitalAccountUnitsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:to="loc_us-gaap_LimitedPartnersCapitalAccountUnitsIssued_019e2887-1480-74e0-99b2-b70654fab4fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding_019e2887-1480-7160-97a4-d014872d8535" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:to="loc_us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding_019e2887-1480-7160-97a4-d014872d8535" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnersCapitalAccountUnitsIssued_019e2887-1480-70fb-8b99-39952620a25d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnersCapitalAccountUnitsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:to="loc_us-gaap_GeneralPartnersCapitalAccountUnitsIssued_019e2887-1480-70fb-8b99-39952620a25d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnersCapitalAccountUnitsOutstanding_019e2887-1480-7367-9f64-3dfe688da25a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnersCapitalAccountUnitsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-749d-93dd-c13bc8381a13" xlink:to="loc_us-gaap_GeneralPartnersCapitalAccountUnitsOutstanding_019e2887-1480-7367-9f64-3dfe688da25a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedStatementsofComprehensiveIncomeLP" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedStatementsofComprehensiveIncomeLP"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedStatementsofComprehensiveIncomeLP" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-7124-84c9-412d4d7a2c62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-7124-84c9-412d4d7a2c62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-776d-a244-f356f8033243" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7124-84c9-412d4d7a2c62" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-776d-a244-f356f8033243" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-776d-a244-f356f8033243_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-776d-a244-f356f8033243" xlink:to="loc_dei_EntityDomain_019e2887-1480-776d-a244-f356f8033243_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-75d4-8f18-264caf644c45" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-776d-a244-f356f8033243" xlink:to="loc_dei_EntityDomain_019e2887-1480-75d4-8f18-264caf644c45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7aee-8d7b-6286982c64c1" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-75d4-8f18-264caf644c45" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7aee-8d7b-6286982c64c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-790c-971f-52c0928536fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7124-84c9-412d4d7a2c62" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-790c-971f-52c0928536fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-790c-971f-52c0928536fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-790c-971f-52c0928536fe" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-790c-971f-52c0928536fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7625-9e2f-68f833a34be1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-790c-971f-52c0928536fe" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7625-9e2f-68f833a34be1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnerMember_019e2887-1480-71f4-a9a6-d4a28b79ec1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7625-9e2f-68f833a34be1" xlink:to="loc_us-gaap_LimitedPartnerMember_019e2887-1480-71f4-a9a6-d4a28b79ec1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnerMember_019e2887-1480-73d9-82b7-35c0c27de8b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7625-9e2f-68f833a34be1" xlink:to="loc_us-gaap_GeneralPartnerMember_019e2887-1480-73d9-82b7-35c0c27de8b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-1480-7d12-ac83-d8232fc3b470" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7124-84c9-412d4d7a2c62" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-1480-7d12-ac83-d8232fc3b470" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-1480-7d12-ac83-d8232fc3b470_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-1480-7d12-ac83-d8232fc3b470" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-1480-7d12-ac83-d8232fc3b470_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-1480-7a07-a5bd-4711ca44155a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-1480-7d12-ac83-d8232fc3b470" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-1480-7a07-a5bd-4711ca44155a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019e2887-1480-72d4-9a23-c140a233a2cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019e2887-1480-7a07-a5bd-4711ca44155a" xlink:to="loc_us-gaap_InterestRateSwapMember_019e2887-1480-72d4-9a23-c140a233a2cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019e2887-1480-70e7-a15f-466846aa1cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_RevenuesAbstract_019e2887-1480-70e7-a15f-466846aa1cd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-1480-7127-aa60-1a1d5a55f556" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e2887-1480-70e7-a15f-466846aa1cd4" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-1480-7127-aa60-1a1d5a55f556" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncome_019e2887-1480-76f1-813b-ba42d982fa17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherOperatingIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e2887-1480-70e7-a15f-466846aa1cd4" xlink:to="loc_us-gaap_OtherOperatingIncome_019e2887-1480-76f1-813b-ba42d982fa17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019e2887-1480-7140-a143-de3ad195c3bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e2887-1480-70e7-a15f-466846aa1cd4" xlink:to="loc_us-gaap_Revenues_019e2887-1480-7140-a143-de3ad195c3bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingCostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-1480-77c7-88a3-2060bdeadb1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfOtherPropertyOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:to="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-1480-77c7-88a3-2060bdeadb1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateTaxExpense_019e2887-1480-7e17-81a9-7c59ceed5e6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateTaxExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:to="loc_us-gaap_RealEstateTaxExpense_019e2887-1480-7e17-81a9-7c59ceed5e6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e2887-1480-7376-aad4-3d21313b49c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e2887-1480-7376-aad4-3d21313b49c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_019e2887-1480-799e-84c9-c389eae49bf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:to="loc_us-gaap_DepreciationAndAmortization_019e2887-1480-799e-84c9-c389eae49bf5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019e2887-1480-76df-b875-f5e761574d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019e2887-1480-798a-bfb8-99d38201fda5" xlink:to="loc_us-gaap_CostsAndExpenses_019e2887-1480-76df-b875-f5e761574d9e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfProperties_019e2887-1480-7aa1-ac63-5b234cc460f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_GainLossOnSaleOfProperties_019e2887-1480-7aa1-ac63-5b234cc460f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e2887-1480-793a-be93-11025de886f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e2887-1480-793a-be93-11025de886f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e2887-1480-7671-b397-7003b0c05371" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e2887-1480-7671-b397-7003b0c05371" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e2887-1480-75ef-b20d-bbccaf0ddf14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e2887-1480-75ef-b20d-bbccaf0ddf14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019e2887-1480-7a43-844e-85bf4bbca1e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_ProfitLoss_019e2887-1480-7a43-844e-85bf4bbca1e3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_NetIncomeAttributableToRestrictedShare_019e2887-1480-7ad4-90ca-88103d8f14aa" xlink:href="aat-20260630.xsd#aat_NetIncomeAttributableToRestrictedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_aat_NetIncomeAttributableToRestrictedShare_019e2887-1480-7ad4-90ca-88103d8f14aa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019e2887-1480-778e-ab9e-de7cb575d6ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019e2887-1480-778e-ab9e-de7cb575d6ba" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_019e2887-1480-7d0a-b90d-451d12de6ee4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_019e2887-1480-7d0a-b90d-451d12de6ee4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019e2887-1480-7f48-a9fe-9f751293b4c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_019e2887-1480-7d0a-b90d-451d12de6ee4" xlink:to="loc_us-gaap_EarningsPerShareBasic_019e2887-1480-7f48-a9fe-9f751293b4c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e2887-1480-769d-94e6-385926754053" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_019e2887-1480-7d0a-b90d-451d12de6ee4" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e2887-1480-769d-94e6-385926754053" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedAbstract_019e2887-1480-7c03-a21b-c26b4c0ac3d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_EarningsPerShareDilutedAbstract_019e2887-1480-7c03-a21b-c26b4c0ac3d1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019e2887-1480-7091-ac10-f088ec748ad3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_019e2887-1480-7c03-a21b-c26b4c0ac3d1" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019e2887-1480-7091-ac10-f088ec748ad3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e2887-1480-7511-9c88-7f8d890c3cc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_019e2887-1480-7c03-a21b-c26b4c0ac3d1" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e2887-1480-7511-9c88-7f8d890c3cc4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DistributionsPerLimitedPartnershipAndGeneralPartnershipUnitOutstandingBasic_019e2887-1480-7088-af1d-70febf98a4c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DistributionsPerLimitedPartnershipAndGeneralPartnershipUnitOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_DistributionsPerLimitedPartnershipAndGeneralPartnershipUnitOutstandingBasic_019e2887-1480-7088-af1d-70febf98a4c6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-79a3-983e-5c26a7927139" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019e2887-1480-739f-83a3-47d3939390ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-7ec1-a461-ab473731d377" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-7ec1-a461-ab473731d377" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-7d34-a670-2b34be9f586d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-7d34-a670-2b34be9f586d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019e2887-1480-75d4-a75f-f8d68ec9941e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019e2887-1480-75d4-a75f-f8d68ec9941e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019e2887-1480-7df5-908e-ca4335f9940d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_019e2887-1480-7e73-8200-2e365299df56" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019e2887-1480-7df5-908e-ca4335f9940d" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedStatementofPartnersCapitalLP" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedStatementofPartnersCapitalLP"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedStatementofPartnersCapitalLP" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-7afb-8897-c8043a288f68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-7786-beb5-64e44403b940" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7afb-8897-c8043a288f68" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-7786-beb5-64e44403b940" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-785b-8947-ad7c375fb68f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7786-beb5-64e44403b940" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-785b-8947-ad7c375fb68f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-785b-8947-ad7c375fb68f_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-785b-8947-ad7c375fb68f" xlink:to="loc_dei_EntityDomain_019e2887-1480-785b-8947-ad7c375fb68f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7bed-9efe-b1b948f8c501" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-785b-8947-ad7c375fb68f" xlink:to="loc_dei_EntityDomain_019e2887-1480-7bed-9efe-b1b948f8c501" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7513-83fd-8c1f0fb00d5d" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-7bed-9efe-b1b948f8c501" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7513-83fd-8c1f0fb00d5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-791e-b336-f3bad0ce9353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7786-beb5-64e44403b940" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-791e-b336-f3bad0ce9353" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-791e-b336-f3bad0ce9353_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-791e-b336-f3bad0ce9353" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-791e-b336-f3bad0ce9353_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7433-a83d-ee4f2959d268" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-1480-791e-b336-f3bad0ce9353" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7433-a83d-ee4f2959d268" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnerMember_019e2887-1480-71c1-a70e-33fcae30ea20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7433-a83d-ee4f2959d268" xlink:to="loc_us-gaap_LimitedPartnerMember_019e2887-1480-71c1-a70e-33fcae30ea20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnerMember_019e2887-1480-76b2-9ae3-1123109c258d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-1480-7433-a83d-ee4f2959d268" xlink:to="loc_us-gaap_GeneralPartnerMember_019e2887-1480-76b2-9ae3-1123109c258d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerCapitalComponentsAxis_019e2887-1480-7a80-a59b-6da7443ed930" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerCapitalComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7786-beb5-64e44403b940" xlink:to="loc_us-gaap_PartnerCapitalComponentsAxis_019e2887-1480-7a80-a59b-6da7443ed930" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerCapitalComponentsDomain_019e2887-1480-7a80-a59b-6da7443ed930_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerCapitalComponentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PartnerCapitalComponentsAxis_019e2887-1480-7a80-a59b-6da7443ed930" xlink:to="loc_us-gaap_PartnerCapitalComponentsDomain_019e2887-1480-7a80-a59b-6da7443ed930_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerCapitalComponentsDomain_019e2887-1480-749b-b295-dfc88d56ab29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerCapitalComponentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PartnerCapitalComponentsAxis_019e2887-1480-7a80-a59b-6da7443ed930" xlink:to="loc_us-gaap_PartnerCapitalComponentsDomain_019e2887-1480-749b-b295-dfc88d56ab29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2887-1480-708f-b5d8-6f16bf7c75e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerCapitalComponentsDomain_019e2887-1480-749b-b295-dfc88d56ab29" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2887-1480-708f-b5d8-6f16bf7c75e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPartnersCapitalRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7afb-8897-c8043a288f68" xlink:to="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountUnits_019e2887-1480-7c96-9641-f4d4eedecd21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapitalAccountUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_PartnersCapitalAccountUnits_019e2887-1480-7c96-9641-f4d4eedecd21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapital_019e2887-1480-7059-b248-9c44711e2109" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_PartnersCapital_019e2887-1480-7059-b248-9c44711e2109" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019e2887-1480-7291-b09e-b2b32a330ad0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_ProfitLoss_019e2887-1480-7291-b09e-b2b32a330ad0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019e40aa-5949-7f10-80f9-f1f0f0e0f9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019e40aa-5949-7f10-80f9-f1f0f0e0f9ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_019e40aa-5949-7c5d-a714-df800079aacd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_019e40aa-5949-7c5d-a714-df800079aacd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PartnersCapitalAccountRestrictedUnitsForfeiture_019e2887-1480-77c3-b74f-c097b52110f4" xlink:href="aat-20260630.xsd#aat_PartnersCapitalAccountRestrictedUnitsForfeiture"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_aat_PartnersCapitalAccountRestrictedUnitsForfeiture_019e2887-1480-77c3-b74f-c097b52110f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountDistributions_019e2887-1480-751e-815b-2a82911c1424" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapitalAccountDistributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_PartnersCapitalAccountDistributions_019e2887-1480-751e-815b-2a82911c1424" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountUnitBasedCompensation_019e2887-1480-773e-837b-8864379e7c28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapitalAccountUnitBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_PartnersCapitalAccountUnitBasedCompensation_019e2887-1480-773e-837b-8864379e7c28" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-749a-8c14-52b4c07bfec4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019e2887-1480-749a-8c14-52b4c07bfec4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-77d3-87c8-1c77c1522fc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInPartnersCapitalRollForward_019e2887-1480-7ae6-b2b2-f0f92429bee0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019e2887-1480-77d3-87c8-1c77c1522fc4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountUnits_019e2887-1480-7ca5-a045-9bc7f03d797b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapitalAccountUnits"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapital_019e2887-1480-73ea-ae5a-930136586bc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnersCapital"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ConsolidatedStatementsofCashFlowsLP" xlink:type="simple" xlink:href="aat-20260630.xsd#ConsolidatedStatementsofCashFlowsLP"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ConsolidatedStatementsofCashFlowsLP" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e2887-1480-7a23-9657-acedce5cd38e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_StatementTable_019e2887-1480-7a23-9657-acedce5cd38e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-1480-7ee8-9cd6-a276d1cca902" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2887-1480-7a23-9657-acedce5cd38e" xlink:to="loc_dei_LegalEntityAxis_019e2887-1480-7ee8-9cd6-a276d1cca902" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7ee8-9cd6-a276d1cca902_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-7ee8-9cd6-a276d1cca902" xlink:to="loc_dei_EntityDomain_019e2887-1480-7ee8-9cd6-a276d1cca902_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-1480-7642-83bf-31de2a6fc83b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-1480-7ee8-9cd6-a276d1cca902" xlink:to="loc_dei_EntityDomain_019e2887-1480-7642-83bf-31de2a6fc83b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7da7-a078-6e86610db53f" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-1480-7642-83bf-31de2a6fc83b" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-1480-7da7-a078-6e86610db53f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-76d9-bb39-66783b615a88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-76d9-bb39-66783b615a88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019e2887-1480-70b1-ab75-a0f2673d96b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-76d9-bb39-66783b615a88" xlink:to="loc_us-gaap_ProfitLoss_019e2887-1480-70b1-ab75-a0f2673d96b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-76d9-bb39-66783b615a88" xlink:to="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DeferredRentRevenueAndAmortizationOfLeaseIntangibles_019e2887-1480-734e-be57-4428da8aaadc" xlink:href="aat-20260630.xsd#aat_DeferredRentRevenueAndAmortizationOfLeaseIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_aat_DeferredRentRevenueAndAmortizationOfLeaseIntangibles_019e2887-1480-734e-be57-4428da8aaadc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019e2887-1480-7f35-9bb7-7804b983c617" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019e2887-1480-7f35-9bb7-7804b983c617" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019e2887-1480-7282-a115-ffc023cdb0de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019e2887-1480-7282-a115-ffc023cdb0de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentInLeaseCreditLossExpenseReversal_019e2887-1480-7c51-a873-60bf45ea517a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentInLeaseCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_NetInvestmentInLeaseCreditLossExpenseReversal_019e2887-1480-7c51-a873-60bf45ea517a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfProperties_019e2887-1480-71f5-af32-06ad303c5a3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_GainLossOnSaleOfProperties_019e2887-1480-71f5-af32-06ad303c5a3a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019e2887-1480-7705-8466-80b082b014d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_ShareBasedCompensation_019e2887-1480-7705-8466-80b082b014d0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnTerminationOfLease_019e3fdb-b32d-7f7d-b1ef-cc8d1e0bd53f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnTerminationOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_GainLossOnTerminationOfLease_019e3fdb-b32d-7f7d-b1ef-cc8d1e0bd53f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OtherNonCashInterestExpense_019e2887-1480-7a8e-8465-45b0ca5ef734" xlink:href="aat-20260630.xsd#aat_OtherNonCashInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_aat_OtherNonCashInterestExpense_019e2887-1480-7a8e-8465-45b0ca5ef734" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_019e2887-1480-7048-a267-5f2380403e19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNoncashIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_019e2887-1480-7048-a267-5f2380403e19" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-70a1-8159-25bf8e259f78" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019e2887-1480-7114-b667-3b2d5a7147e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019e2887-1480-7114-b667-3b2d5a7147e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019e2887-1480-7364-bf7e-24bbfaf0e180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019e2887-1480-7364-bf7e-24bbfaf0e180" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_019e2887-1480-7fa5-93df-8650173957c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_019e2887-1480-7fa5-93df-8650173957c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_IncreaseDecreaseInSecurityDepositsPayable_019e2887-1480-79a1-b749-932dee7d6a0a" xlink:href="aat-20260630.xsd#aat_IncreaseDecreaseInSecurityDepositsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:to="loc_aat_IncreaseDecreaseInSecurityDepositsPayable_019e2887-1480-79a1-b749-932dee7d6a0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherDeferredLiability_019e2887-1480-7100-bdf3-ed0a36c458d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherDeferredLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019e2887-1480-7250-85b2-b14a604a03cc" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherDeferredLiability_019e2887-1480-7100-bdf3-ed0a36c458d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019e2887-1480-7f8d-b087-757e32aea07a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019e2887-1480-76d9-bb39-66783b615a88" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019e2887-1480-7f8d-b087-757e32aea07a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireCommercialRealEstate_019e2887-1480-7c10-9c66-dc47428e6075" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireCommercialRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:to="loc_us-gaap_PaymentsToAcquireCommercialRealEstate_019e2887-1480-7c10-9c66-dc47428e6075" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForCapitalImprovements_019e2887-1480-76b0-8315-3d0fcfacf252" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForCapitalImprovements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:to="loc_us-gaap_PaymentsForCapitalImprovements_019e2887-1480-76b0-8315-3d0fcfacf252" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfRealEstateHeldforinvestment_019e2887-1480-7e74-9972-7fe858d7a262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfRealEstateHeldforinvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:to="loc_us-gaap_ProceedsFromSaleOfRealEstateHeldforinvestment_019e2887-1480-7e74-9972-7fe858d7a262" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInLeaseAcquisitionCosts_019e2887-1480-7f92-a507-2192defa482f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInLeaseAcquisitionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:to="loc_us-gaap_IncreaseDecreaseInLeaseAcquisitionCosts_019e2887-1480-7f92-a507-2192defa482f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019e2887-1480-7524-969a-267d13f92f02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019e2887-1480-7ae4-a9b1-fb6d8c27a997" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019e2887-1480-7524-969a-267d13f92f02" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfUnsecuredDebt_019e2887-1480-76af-b441-e55d7f25cbf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfUnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:to="loc_us-gaap_RepaymentsOfUnsecuredDebt_019e2887-1480-76af-b441-e55d7f25cbf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfNotesPayable_019e2887-1480-7469-afc4-1ab60f37086c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:to="loc_us-gaap_RepaymentsOfNotesPayable_019e2887-1480-7469-afc4-1ab60f37086c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_019f596b-b2ff-7688-92e3-9399266a1b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_019f596b-b2ff-7688-92e3-9399266a1b7e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019e2887-1480-72b0-8c86-2546e6380696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:to="loc_us-gaap_PaymentsOfDividends_019e2887-1480-72b0-8c86-2546e6380696" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019e2887-1480-7e4c-bcb6-abb05d601a4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019e2887-1480-788f-8aa5-d528eeae8079" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019e2887-1480-7e4c-bcb6-abb05d601a4a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019e2887-1480-7536-802a-3b04b66ec922" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019e2887-1480-7536-802a-3b04b66ec922" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019e2887-1480-74b5-ace7-8eb5cdbf9dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2887-1480-7d31-9467-178a4a347e37" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019e2887-1480-74b5-ace7-8eb5cdbf9dd7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019e2887-1480-74c0-b2f2-1c32a7cc296f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019e2887-1480-77fa-90b3-6d013be31b73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019e2887-1480-77fa-90b3-6d013be31b73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-1480-729f-98b1-c331b12ff4cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019e2887-1480-77fa-90b3-6d013be31b73" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-1480-729f-98b1-c331b12ff4cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-729f-98b1-c331b12ff4cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-1480-729f-98b1-c331b12ff4cd" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-729f-98b1-c331b12ff4cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-7ad8-a644-a0c5b9c916a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-1480-729f-98b1-c331b12ff4cd" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-7ad8-a644-a0c5b9c916a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeasesAcquiredInPlaceMember_019e2887-1480-7f78-af8b-d3cd4a611b24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeasesAcquiredInPlaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-7ad8-a644-a0c5b9c916a6" xlink:to="loc_us-gaap_LeasesAcquiredInPlaceMember_019e2887-1480-7f78-af8b-d3cd4a611b24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AboveMarketLeasesMember_019e2887-1480-7f43-a635-dc1259a4353d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AboveMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-1480-7ad8-a644-a0c5b9c916a6" xlink:to="loc_us-gaap_AboveMarketLeasesMember_019e2887-1480-7f43-a635-dc1259a4353d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetOffMarketLeaseFavorableGross_019e2887-1480-7fba-abfd-10dc8eb29461" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetOffMarketLeaseFavorableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetOffMarketLeaseFavorableGross_019e2887-1480-7fba-abfd-10dc8eb29461" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e2887-1480-726b-813b-910e6b245033" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e2887-1480-726b-813b-910e6b245033" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e2887-1480-7529-8af8-1244a66f30ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e2887-1480-7529-8af8-1244a66f30ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseGross_019e2887-1480-743c-866b-79e94b488678" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BelowMarketLeaseGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_BelowMarketLeaseGross_019e2887-1480-743c-866b-79e94b488678" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAccumulatedAmortization_019e2887-1480-7411-9693-3ec642c5b3d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BelowMarketLeaseAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_BelowMarketLeaseAccumulatedAmortization_019e2887-1480-7411-9693-3ec642c5b3d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseNet_019e2887-1480-731f-82f5-0e8ea299afc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BelowMarketLeaseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019e2887-1480-7160-9faa-275e8f3ab073" xlink:to="loc_us-gaap_BelowMarketLeaseNet_019e2887-1480-731f-82f5-0e8ea299afc3" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2887-1480-7717-9e90-62bb2fb55b47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2887-1480-7e21-915c-a9353f1fbde2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2887-1480-7717-9e90-62bb2fb55b47" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2887-1480-7e21-915c-a9353f1fbde2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-759d-9455-2bc5b91f75dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2887-1480-7e21-915c-a9353f1fbde2" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-759d-9455-2bc5b91f75dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-759d-9455-2bc5b91f75dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-759d-9455-2bc5b91f75dc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-759d-9455-2bc5b91f75dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-746b-97f4-dce63bf6214f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-759d-9455-2bc5b91f75dc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-746b-97f4-dce63bf6214f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e2887-1480-7996-86b2-dfd6d899fcac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-746b-97f4-dce63bf6214f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e2887-1480-7996-86b2-dfd6d899fcac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e2887-1480-7aa0-b6f0-3d5eae0b0f78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-746b-97f4-dce63bf6214f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e2887-1480-7aa0-b6f0-3d5eae0b0f78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e2887-1480-7420-9e41-85394d263b51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-746b-97f4-dce63bf6214f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e2887-1480-7420-9e41-85394d263b51" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019e2887-1480-7e85-bc30-e32bbf555495" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2887-1480-7717-9e90-62bb2fb55b47" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019e2887-1480-7e85-bc30-e32bbf555495" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_019e2887-1480-7e53-9c08-c2fd326bc492" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2887-1480-7717-9e90-62bb2fb55b47" xlink:to="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_019e2887-1480-7e53-9c08-c2fd326bc492" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSNarrativeDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#FAIRVALUEOFFINANCIALINSTRUMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e2887-153a-7c30-ae02-4d857218d0ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e2887-1480-7f54-a5a1-51e8a95d1220" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e2887-153a-7c30-ae02-4d857218d0ac" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e2887-1480-7f54-a5a1-51e8a95d1220" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-7495-b4fb-cf00ed94dc57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e2887-1480-7f54-a5a1-51e8a95d1220" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-7495-b4fb-cf00ed94dc57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-7495-b4fb-cf00ed94dc57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-7495-b4fb-cf00ed94dc57" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-7495-b4fb-cf00ed94dc57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-7eba-a586-8a6b5c3fa60e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-1480-7495-b4fb-cf00ed94dc57" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-7eba-a586-8a6b5c3fa60e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e2887-1480-7f9a-af04-52f0ce25090e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-1480-7eba-a586-8a6b5c3fa60e" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e2887-1480-7f9a-af04-52f0ce25090e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e2887-1480-7336-ba40-26c29eadebe9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e2887-1480-7f54-a5a1-51e8a95d1220" xlink:to="loc_srt_RangeAxis_019e2887-1480-7336-ba40-26c29eadebe9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-1480-7336-ba40-26c29eadebe9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e2887-1480-7336-ba40-26c29eadebe9" xlink:to="loc_srt_RangeMember_019e2887-1480-7336-ba40-26c29eadebe9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-1480-7afd-9bc7-c4cd13f2d67e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e2887-1480-7336-ba40-26c29eadebe9" xlink:to="loc_srt_RangeMember_019e2887-1480-7afd-9bc7-c4cd13f2d67e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e2887-153a-73aa-bc91-f0080921811d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e2887-1480-7afd-9bc7-c4cd13f2d67e" xlink:to="loc_srt_MinimumMember_019e2887-153a-73aa-bc91-f0080921811d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e2887-153a-78d8-837b-11b8d58056c8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e2887-1480-7afd-9bc7-c4cd13f2d67e" xlink:to="loc_srt_MaximumMember_019e2887-153a-78d8-837b-11b8d58056c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentMeasurementInput_019e2887-153a-74e0-8236-da24c54e5f3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e2887-153a-7c30-ae02-4d857218d0ac" xlink:to="loc_us-gaap_DebtInstrumentMeasurementInput_019e2887-153a-74e0-8236-da24c54e5f3b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofCarryingAmountandFairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofCarryingAmountandFairValueofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofCarryingAmountandFairValueofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2887-153b-7207-9a33-1b49eee668e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2887-153b-7207-9a33-1b49eee668e1" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153a-721d-84d1-2cca3459c23f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153a-721d-84d1-2cca3459c23f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153a-721d-84d1-2cca3459c23f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153a-721d-84d1-2cca3459c23f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153a-721d-84d1-2cca3459c23f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7fc4-94ce-c6cb7172a443" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153a-721d-84d1-2cca3459c23f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7fc4-94ce-c6cb7172a443" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e2887-153b-7ec7-ba54-31ba065f8f3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7fc4-94ce-c6cb7172a443" xlink:to="loc_us-gaap_SecuredDebtMember_019e2887-153b-7ec7-ba54-31ba065f8f3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019e2887-153b-7da2-b04c-914c61766f49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7fc4-94ce-c6cb7172a443" xlink:to="loc_us-gaap_UnsecuredDebtMember_019e2887-153b-7da2-b04c-914c61766f49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019e2887-153b-7367-9458-4473782d3e34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7fc4-94ce-c6cb7172a443" xlink:to="loc_us-gaap_SeniorNotesMember_019e2887-153b-7367-9458-4473782d3e34" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2887-153b-7950-9c5d-f43b3110edba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2887-153b-7950-9c5d-f43b3110edba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-7950-9c5d-f43b3110edba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2887-153b-7950-9c5d-f43b3110edba" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-7950-9c5d-f43b3110edba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2887-153b-71f0-9b18-57095803ecac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2887-153b-7950-9c5d-f43b3110edba" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2887-153b-71f0-9b18-57095803ecac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-713b-a53f-545bfec32b38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2887-153b-71f0-9b18-57095803ecac" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-713b-a53f-545bfec32b38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e2887-153b-7119-8685-0e9b247b056d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-713b-a53f-545bfec32b38" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e2887-153b-7119-8685-0e9b247b056d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e2887-153b-7273-b24f-7fe23a52a72c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2887-153b-713b-a53f-545bfec32b38" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e2887-153b-7273-b24f-7fe23a52a72c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-153b-77bb-ad44-69e01856adeb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-153b-77bb-ad44-69e01856adeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-153b-77bb-ad44-69e01856adeb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-153b-77bb-ad44-69e01856adeb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-153b-77bb-ad44-69e01856adeb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-153b-76f9-b2c5-1c38b28cab98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2887-153b-77bb-ad44-69e01856adeb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-153b-76f9-b2c5-1c38b28cab98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e2887-153b-7e4f-b18c-9bb7a349e6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2887-153b-76f9-b2c5-1c38b28cab98" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e2887-153b-7e4f-b18c-9bb7a349e6b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7f1b-a38b-8793b766d4e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2887-153a-7668-b36a-364b643016f0" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7f1b-a38b-8793b766d4e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7f1b-a38b-8793b766d4e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7f1b-a38b-8793b766d4e1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7f1b-a38b-8793b766d4e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7a9e-b95a-318a0b01c228" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7f1b-a38b-8793b766d4e1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7a9e-b95a-318a0b01c228" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A3375SeniorUnsecuredNotesMember_019e2887-153b-7c44-94a9-987780cc59ea" xlink:href="aat-20260630.xsd#aat_A3375SeniorUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7a9e-b95a-318a0b01c228" xlink:to="loc_aat_A3375SeniorUnsecuredNotesMember_019e2887-153b-7c44-94a9-987780cc59ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019e2887-153b-7ad5-a6e9-58d5ff5b6f59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2887-153b-7207-9a33-1b49eee668e1" xlink:to="loc_us-gaap_LongTermDebtFairValue_019e2887-153b-7ad5-a6e9-58d5ff5b6f59" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIESSummaryofInterestRateSwapTermsDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#DERIVATIVEANDHEDGINGACTIVITIESSummaryofInterestRateSwapTermsDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIESSummaryofInterestRateSwapTermsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019e2887-153b-79fa-9be9-25bc9d66896b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019e2887-153b-79fa-9be9-25bc9d66896b" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e2887-153b-79c7-8d8d-2931e775eb52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:to="loc_srt_CounterpartyNameAxis_019e2887-153b-79c7-8d8d-2931e775eb52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-79c7-8d8d-2931e775eb52_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019e2887-153b-79c7-8d8d-2931e775eb52" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-79c7-8d8d-2931e775eb52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-711f-97e9-afb8f91c1f6b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019e2887-153b-79c7-8d8d-2931e775eb52" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-711f-97e9-afb8f91c1f6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_BankOfAmericaNAMember_019e2887-153b-7cbb-bb20-a2655d7ed3d7" xlink:href="aat-20260630.xsd#aat_BankOfAmericaNAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-711f-97e9-afb8f91c1f6b" xlink:to="loc_aat_BankOfAmericaNAMember_019e2887-153b-7cbb-bb20-a2655d7ed3d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_WellsFargoBankN.A.Member_019e2887-153b-7e07-9e54-31e57a511d81" xlink:href="aat-20260630.xsd#aat_WellsFargoBankN.A.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-711f-97e9-afb8f91c1f6b" xlink:to="loc_aat_WellsFargoBankN.A.Member_019e2887-153b-7e07-9e54-31e57a511d81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-75bd-a936-bb4ffe7e88cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-75bd-a936-bb4ffe7e88cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-75bd-a936-bb4ffe7e88cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-75bd-a936-bb4ffe7e88cb" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-75bd-a936-bb4ffe7e88cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7567-9dd2-8d0fbb87ac40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-75bd-a936-bb4ffe7e88cb" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7567-9dd2-8d0fbb87ac40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_InterestRateSwap152027Member_019e2887-153b-71e7-b995-71973f1ad52e" xlink:href="aat-20260630.xsd#aat_InterestRateSwap152027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7567-9dd2-8d0fbb87ac40" xlink:to="loc_aat_InterestRateSwap152027Member_019e2887-153b-71e7-b995-71973f1ad52e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019e2887-153b-7495-ac3b-22e63cb09356" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019e2887-153b-7495-ac3b-22e63cb09356" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019e2887-153b-7495-ac3b-22e63cb09356_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019e2887-153b-7495-ac3b-22e63cb09356" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019e2887-153b-7495-ac3b-22e63cb09356_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019e2887-153b-7c9f-a69d-93a46d5a27b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019e2887-153b-7495-ac3b-22e63cb09356" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019e2887-153b-7c9f-a69d-93a46d5a27b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019e2887-153b-7490-a708-bf29966d2b32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019e2887-153b-7c9f-a69d-93a46d5a27b2" xlink:to="loc_us-gaap_CashFlowHedgingMember_019e2887-153b-7490-a708-bf29966d2b32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019e2887-153b-78b2-9ee5-7bcdb469cbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:to="loc_us-gaap_HedgingDesignationAxis_019e2887-153b-78b2-9ee5-7bcdb469cbb8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019e2887-153b-78b2-9ee5-7bcdb469cbb8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019e2887-153b-78b2-9ee5-7bcdb469cbb8" xlink:to="loc_us-gaap_HedgingDesignationDomain_019e2887-153b-78b2-9ee5-7bcdb469cbb8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019e2887-153b-739a-983e-0eb093145bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019e2887-153b-78b2-9ee5-7bcdb469cbb8" xlink:to="loc_us-gaap_HedgingDesignationDomain_019e2887-153b-739a-983e-0eb093145bfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019e2887-153b-78b7-8d43-29189cb59578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019e2887-153b-739a-983e-0eb093145bfb" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019e2887-153b-78b7-8d43-29189cb59578" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-70c4-bfed-5e384bc3e9bb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019e2887-153b-7ecf-a0c2-20fc51aac024" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-70c4-bfed-5e384bc3e9bb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-70c4-bfed-5e384bc3e9bb_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-70c4-bfed-5e384bc3e9bb" xlink:to="loc_dei_EntityDomain_019e2887-153b-70c4-bfed-5e384bc3e9bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-76d9-96e7-e981a4d97f29" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-70c4-bfed-5e384bc3e9bb" xlink:to="loc_dei_EntityDomain_019e2887-153b-76d9-96e7-e981a4d97f29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-786d-be5d-50dfddd2fe9c" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-76d9-96e7-e981a4d97f29" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-786d-be5d-50dfddd2fe9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019e2887-153b-7c76-b198-2ead642bd7ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019e2887-153b-79fa-9be9-25bc9d66896b" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019e2887-153b-7c76-b198-2ead642bd7ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_019e2887-153b-78ff-8403-9f23728bbd14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019e2887-153b-79fa-9be9-25bc9d66896b" xlink:to="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_019e2887-153b-78ff-8403-9f23728bbd14" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/OTHERASSETSNETDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#OTHERASSETSNETDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/OTHERASSETSNETDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e2887-153b-77e3-8247-6913a9c27c12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e2887-153b-77e3-8247-6913a9c27c12" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-153b-7d94-81a4-9b6364adce88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e2887-153b-77e3-8247-6913a9c27c12" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-153b-7d94-81a4-9b6364adce88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7d94-81a4-9b6364adce88_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-153b-7d94-81a4-9b6364adce88" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7d94-81a4-9b6364adce88_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7f70-af81-01247efb4af4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e2887-153b-7d94-81a4-9b6364adce88" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7f70-af81-01247efb4af4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AboveMarketLeasesMember_019e2887-153b-7ad7-b86f-0e4af119b29f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AboveMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7f70-af81-01247efb4af4" xlink:to="loc_us-gaap_AboveMarketLeasesMember_019e2887-153b-7ad7-b86f-0e4af119b29f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeasesAcquiredInPlaceMember_019e2887-153b-7427-a5c3-9b351abd8961" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeasesAcquiredInPlaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e2887-153b-7f70-af81-01247efb4af4" xlink:to="loc_us-gaap_LeasesAcquiredInPlaceMember_019e2887-153b-7427-a5c3-9b351abd8961" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsLeasingNet_019e2887-153b-7862-be02-30b09dac6af7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCostsLeasingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_DeferredCostsLeasingNet_019e2887-153b-7862-be02-30b09dac6af7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019e2887-153b-7a85-bdb7-642e69a7d391" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_DerivativeAssets_019e2887-153b-7a85-bdb7-642e69a7d391" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019e2887-153b-7776-a092-71b2c7d7c51d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssets_019e2887-153b-7a85-bdb7-642e69a7d391" xlink:to="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019e2887-153b-7776-a092-71b2c7d7c51d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e2887-153b-7a3c-b3d9-dcb8afed920c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e2887-153b-7a3c-b3d9-dcb8afed920c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveToLessee_019e2887-153b-736c-86d6-e0bb62374be0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncentiveToLessee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_IncentiveToLessee_019e2887-153b-736c-86d6-e0bb62374be0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherFiniteLivedIntangibleAssetsGross_019e2887-153b-76be-af14-c00fc031eb20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherFiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_OtherFiniteLivedIntangibleAssetsGross_019e2887-153b-76be-af14-c00fc031eb20" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-746a-b1f4-615b33a84a9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-746a-b1f4-615b33a84a9a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e2887-153b-7869-a73c-6fab8ee99f30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e2887-153b-7869-a73c-6fab8ee99f30" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_019e2887-153b-732e-8ead-3d68034d88e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e2887-153b-7869-a73c-6fab8ee99f30" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_019e2887-153b-732e-8ead-3d68034d88e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseCurrentAndNoncurrent_019e2887-153b-7036-98c7-3e29aa48d1ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_PrepaidExpenseCurrentAndNoncurrent_019e2887-153b-7036-98c7-3e29aa48d1ca" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_019e2887-153b-7f54-bf03-0fd1740501de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_OtherAssets_019e2887-153b-7f54-bf03-0fd1740501de" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsLeasingAccumulatedAmortization_019e2887-153b-7c13-be14-b9e9b48d3789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCostsLeasingAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_DeferredCostsLeasingAccumulatedAmortization_019e2887-153b-7c13-be14-b9e9b48d3789" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_LeaseIncentiveAccumulatedAmortization_019e2887-153b-73de-a72a-7ff94834db98" xlink:href="aat-20260630.xsd#aat_LeaseIncentiveAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_aat_LeaseIncentiveAccumulatedAmortization_019e2887-153b-73de-a72a-7ff94834db98" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e2887-153b-7166-9e36-4fe5d3ca31bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e2887-153b-7166-9e36-4fe5d3ca31bd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-785a-bea9-8021fba5c951" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e2887-153b-7b51-84ea-7bcccb554176" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-785a-bea9-8021fba5c951" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ea6ce-8630-7f3a-8a4a-dfe0eb060a24" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A3375SeniorUnsecuredNotesMember_019ea6ce-8630-704e-b726-f3f2362beec2" xlink:href="aat-20260630.xsd#aat_A3375SeniorUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_A3375SeniorUnsecuredNotesMember_019ea6ce-8630-704e-b726-f3f2362beec2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A6.150SeniorUnsecuredNotesMember_019ea6ce-8630-7f6b-9a40-d547d70de4e6" xlink:href="aat-20260630.xsd#aat_A6.150SeniorUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_A6.150SeniorUnsecuredNotesMember_019ea6ce-8630-7f6b-9a40-d547d70de4e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesAMember_019ea6ce-d40d-7865-9f64-67902965d53a" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesAMember_019ea6ce-d40d-7865-9f64-67902965d53a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SecondAmendedandRestatedCreditFacilityMember_019ea6ce-d40d-7b2b-80c2-e5e4390d92c9" xlink:href="aat-20260630.xsd#aat_SecondAmendedandRestatedCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SecondAmendedandRestatedCreditFacilityMember_019ea6ce-d40d-7b2b-80c2-e5e4390d92c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RevolverLoanMember_019ea6cf-2c6a-7863-a3c9-43473f824508" xlink:href="aat-20260630.xsd#aat_RevolverLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_RevolverLoanMember_019ea6cf-2c6a-7863-a3c9-43473f824508" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesBMember_019ea6cf-2c6a-7bda-b0b3-6cdcacd213e6" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesBMember_019ea6cf-2c6a-7bda-b0b3-6cdcacd213e6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesCMember_019ea6cf-2c6a-7d2b-b445-b23896ccf840" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesCMember_019ea6cf-2c6a-7d2b-b445-b23896ccf840" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesDMember_019ea6cf-6ec9-73d3-8525-97d5992d90fb" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesDMember_019ea6cf-6ec9-73d3-8525-97d5992d90fb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesEMember_019ea6cf-6ec9-7f4f-b483-3d129e498cc1" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesEMember_019ea6cf-6ec9-7f4f-b483-3d129e498cc1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesGMember_019ea6cf-6ec9-7c36-a89a-bf680da41ba1" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesGMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesGMember_019ea6cf-6ec9-7c36-a89a-bf680da41ba1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmendedAndRestatedCreditFacilityMember_019ea6cf-b32c-74a7-b778-65e68793925b" xlink:href="aat-20260630.xsd#aat_AmendedAndRestatedCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ea6ce-8630-7407-a9c6-2ab530bbfde5" xlink:to="loc_aat_AmendedAndRestatedCreditFacilityMember_019ea6cf-b32c-74a7-b778-65e68793925b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ea6ce-8630-78c0-8c7c-cfb507d0173d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_dei_LegalEntityAxis_019ea6ce-8630-78c0-8c7c-cfb507d0173d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ea6ce-8630-78c0-8c7c-cfb507d0173d_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ea6ce-8630-78c0-8c7c-cfb507d0173d" xlink:to="loc_dei_EntityDomain_019ea6ce-8630-78c0-8c7c-cfb507d0173d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ea6ce-8630-7479-91fd-b3896e20b95f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ea6ce-8630-78c0-8c7c-cfb507d0173d" xlink:to="loc_dei_EntityDomain_019ea6ce-8630-7479-91fd-b3896e20b95f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019ea6ce-8630-7367-9a00-d9b81e9a82bb" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ea6ce-8630-7479-91fd-b3896e20b95f" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019ea6ce-8630-7367-9a00-d9b81e9a82bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-701b-868a-5b100733c2cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ea6ce-d40d-72a2-9dc7-3de54e17dbc8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-701b-868a-5b100733c2cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019ea6ce-d40d-7f8e-98e8-921be67dbebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-701b-868a-5b100733c2cb" xlink:to="loc_us-gaap_UnsecuredDebtMember_019ea6ce-d40d-7f8e-98e8-921be67dbebe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ea6cf-b32c-7e2f-b7b2-f822dcc4b5c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ea6ce-d40d-701b-868a-5b100733c2cb" xlink:to="loc_us-gaap_LineOfCreditMember_019ea6cf-b32c-7e2f-b7b2-f822dcc4b5c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019ea6cf-5228-7a73-874c-dcf2ad10ff93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019ea6cf-5228-7a73-874c-dcf2ad10ff93" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019ea6cf-5228-7a73-874c-dcf2ad10ff93_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019ea6cf-5228-7a73-874c-dcf2ad10ff93" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019ea6cf-5228-7a73-874c-dcf2ad10ff93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019ea6cf-5228-7204-afbf-9a748ef34e15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019ea6cf-5228-7a73-874c-dcf2ad10ff93" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019ea6cf-5228-7204-afbf-9a748ef34e15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryLockMember_019ea6cf-5228-7caf-a18c-095ebe23799a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019ea6cf-5228-7204-afbf-9a748ef34e15" xlink:to="loc_us-gaap_TreasuryLockMember_019ea6cf-5228-7caf-a18c-095ebe23799a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ea6cf-b32c-7211-ad7b-3618713d1ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_us-gaap_CreditFacilityAxis_019ea6cf-b32c-7211-ad7b-3618713d1ea5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-7211-ad7b-3618713d1ea5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ea6cf-b32c-7211-ad7b-3618713d1ea5" xlink:to="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-7211-ad7b-3618713d1ea5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-795e-9445-9563ad788f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ea6cf-b32c-7211-ad7b-3618713d1ea5" xlink:to="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-795e-9445-9563ad788f8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019ea6d9-3d55-768b-8a84-226b29f3666c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-795e-9445-9563ad788f8d" xlink:to="loc_us-gaap_UnsecuredDebtMember_019ea6d9-3d55-768b-8a84-226b29f3666c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019ea6cf-b32c-7344-80c2-9ebefa130dcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ea6cf-b32c-795e-9445-9563ad788f8d" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019ea6cf-b32c-7344-80c2-9ebefa130dcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ea6cf-b32c-79bf-b76a-78317f6f49df" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_srt_RangeAxis_019ea6cf-b32c-79bf-b76a-78317f6f49df" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ea6cf-b32c-79bf-b76a-78317f6f49df_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ea6cf-b32c-79bf-b76a-78317f6f49df" xlink:to="loc_srt_RangeMember_019ea6cf-b32c-79bf-b76a-78317f6f49df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ea6cf-b32c-7e7c-a38c-26759c5d9a23" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ea6cf-b32c-79bf-b76a-78317f6f49df" xlink:to="loc_srt_RangeMember_019ea6cf-b32c-7e7c-a38c-26759c5d9a23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ea6cf-b32c-7e17-914e-623dc420e967" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ea6cf-b32c-7e7c-a38c-26759c5d9a23" xlink:to="loc_srt_MinimumMember_019ea6cf-b32c-7e17-914e-623dc420e967" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ea6cf-b32c-7352-b612-a5ee5f8c8b9e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ea6cf-b32c-7e7c-a38c-26759c5d9a23" xlink:to="loc_srt_MaximumMember_019ea6cf-b32c-7352-b612-a5ee5f8c8b9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019ea6cf-b32c-72c9-9b50-cc145b523f8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-72d6-b851-2064b8dd689b" xlink:to="loc_us-gaap_VariableRateAxis_019ea6cf-b32c-72c9-9b50-cc145b523f8a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-72c9-9b50-cc145b523f8a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019ea6cf-b32c-72c9-9b50-cc145b523f8a" xlink:to="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-72c9-9b50-cc145b523f8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019ea6cf-b32c-72c9-9b50-cc145b523f8a" xlink:to="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019ea6cf-b32c-7b4c-be88-148c92789567" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019ea6cf-b32c-7b4c-be88-148c92789567" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_FederalFundsRateMember_019ea6cf-b32c-7f08-bb74-a40444da463a" xlink:href="aat-20260630.xsd#aat_FederalFundsRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:to="loc_aat_FederalFundsRateMember_019ea6cf-b32c-7f08-bb74-a40444da463a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_TermScreenSecuredOvernightFinancingRateSOFRMember_019ea6cf-b32c-7f62-9180-05b8d0dcb8f1" xlink:href="aat-20260630.xsd#aat_TermScreenSecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:to="loc_aat_TermScreenSecuredOvernightFinancingRateSOFRMember_019ea6cf-b32c-7f62-9180-05b8d0dcb8f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019ea6cf-b32c-7e85-af53-53353ff02a11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ea6cf-b32c-7606-b544-e3de3a3991fa" xlink:to="loc_us-gaap_BaseRateMember_019ea6cf-b32c-7e85-af53-53353ff02a11" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ea6ce-8630-7fa6-a436-4a6416db97d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ea6ce-8630-7fa6-a436-4a6416db97d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019ea6ce-d40d-72e9-a700-104d8beea803" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019ea6ce-d40d-72e9-a700-104d8beea803" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentFaceIssuancePercent_019ea6ce-d40d-7a4a-a5ec-6f8f6672b760" xlink:href="aat-20260630.xsd#aat_DebtInstrumentFaceIssuancePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentFaceIssuancePercent_019ea6ce-d40d-7a4a-a5ec-6f8f6672b760" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019ea6ce-d40d-79af-8a4b-63706c53c093" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019ea6ce-d40d-79af-8a4b-63706c53c093" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019ea6ce-d40d-7f55-9841-05dfac2924a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDebtNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019ea6ce-d40d-7f55-9841-05dfac2924a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfUnsecuredDebt_019ea6ce-d40d-79e4-9da5-acdd187fce5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfUnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_RepaymentsOfUnsecuredDebt_019ea6ce-d40d-79e4-9da5-acdd187fce5c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MakeWholePaymentForDebtExtinguishment_019ea6ce-d40d-73cb-a15b-51d40209a586" xlink:href="aat-20260630.xsd#aat_MakeWholePaymentForDebtExtinguishment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MakeWholePaymentForDebtExtinguishment_019ea6ce-d40d-73cb-a15b-51d40209a586" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019ea6ce-d40d-73c2-9ab6-3ec939dd4069" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019ea6ce-d40d-73c2-9ab6-3ec939dd4069" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019ea6cf-5228-7c58-8aff-b2d3f88e08ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019ea6cf-5228-7c58-8aff-b2d3f88e08ba" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentCovenantsMaximumAggregateDebtRatio_019ea6cf-5228-79a0-92f5-db0cfc26c978" xlink:href="aat-20260630.xsd#aat_DebtInstrumentCovenantsMaximumAggregateDebtRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentCovenantsMaximumAggregateDebtRatio_019ea6cf-5228-79a0-92f5-db0cfc26c978" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentCovenantsMinimumDebtServiceRatio_019ea6cf-5228-74ae-906f-896519013cde" xlink:href="aat-20260630.xsd#aat_DebtInstrumentCovenantsMinimumDebtServiceRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentCovenantsMinimumDebtServiceRatio_019ea6cf-5228-74ae-906f-896519013cde" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentCovenantsMaximumSecuredDebtRatio_019ea6cf-5228-794d-bca8-754db66e9620" xlink:href="aat-20260630.xsd#aat_DebtInstrumentCovenantsMaximumSecuredDebtRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentCovenantsMaximumSecuredDebtRatio_019ea6cf-5228-794d-bca8-754db66e9620" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentCovenantsMinimumMaintenanceOfTotalUnencumberedAssets_019ea6cf-5228-7c02-b50e-ca4fd13294a2" xlink:href="aat-20260630.xsd#aat_DebtInstrumentCovenantsMinimumMaintenanceOfTotalUnencumberedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentCovenantsMinimumMaintenanceOfTotalUnencumberedAssets_019ea6cf-5228-7c02-b50e-ca4fd13294a2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentPartialRepaymentMinimumPercentageofPrincipal_019ea6cf-8b2e-79b6-b9ab-a59b329d3729" xlink:href="aat-20260630.xsd#aat_DebtInstrumentPartialRepaymentMinimumPercentageofPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentPartialRepaymentMinimumPercentageofPrincipal_019ea6cf-8b2e-79b6-b9ab-a59b329d3729" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentPrepaymentPercentageOfPrincipal_019ea6cf-8b2e-7a5a-86c3-d1eab229f16a" xlink:href="aat-20260630.xsd#aat_DebtInstrumentPrepaymentPercentageOfPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentPrepaymentPercentageOfPrincipal_019ea6cf-8b2e-7a5a-86c3-d1eab229f16a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ea6cf-b32c-7035-b1e7-a834ab8ee694" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ea6cf-b32c-7035-b1e7-a834ab8ee694" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentExtensionOptions_019ea6cf-b32c-7841-b79f-5bf80578776d" xlink:href="aat-20260630.xsd#aat_DebtInstrumentExtensionOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentExtensionOptions_019ea6cf-b32c-7841-b79f-5bf80578776d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentExtensionTerm_019ea6cf-b32c-7c0e-be6e-4a70a1725bf6" xlink:href="aat-20260630.xsd#aat_DebtInstrumentExtensionTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_DebtInstrumentExtensionTerm_019ea6cf-b32c-7c0e-be6e-4a70a1725bf6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019ea6cf-b32c-7ae8-953a-0af4f695c6c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_LineOfCredit_019ea6cf-b32c-7ae8-953a-0af4f695c6c5" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_019ea6cf-b32c-7a4f-bdf7-348f0f066596" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_019ea6cf-b32c-7a4f-bdf7-348f0f066596" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_019ea6cf-b32c-726b-b4f5-ccef124085c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_019ea6cf-b32c-726b-b4f5-ccef124085c2" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ea6cf-b32c-797f-828c-a23754093c80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ea6cf-b32c-797f-828c-a23754093c80" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_LineOfCreditFacilityMaximumLeveragePercentage_019ea6cf-d0b8-7255-8ed4-2aa8668373aa" xlink:href="aat-20260630.xsd#aat_LineOfCreditFacilityMaximumLeveragePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_LineOfCreditFacilityMaximumLeveragePercentage_019ea6cf-d0b8-7255-8ed4-2aa8668373aa" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MaximumSecuredLeverageRatioOnRevolvingCreditFacility_019ea6cf-d0b8-7d70-9e02-7be920dda7f1" xlink:href="aat-20260630.xsd#aat_MaximumSecuredLeverageRatioOnRevolvingCreditFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MaximumSecuredLeverageRatioOnRevolvingCreditFacility_019ea6cf-d0b8-7d70-9e02-7be920dda7f1" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MinimumFixedChargeCoverageRatioOnRevolvingCreditFacility_019ea6cf-d0b8-7d58-a3fc-f040f2668945" xlink:href="aat-20260630.xsd#aat_MinimumFixedChargeCoverageRatioOnRevolvingCreditFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MinimumFixedChargeCoverageRatioOnRevolvingCreditFacility_019ea6cf-d0b8-7d58-a3fc-f040f2668945" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MinimumUnsecuredInterestCoverageRatio_019ea6cf-d0b8-734c-9e9d-eb30e2ae6b3d" xlink:href="aat-20260630.xsd#aat_MinimumUnsecuredInterestCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MinimumUnsecuredInterestCoverageRatio_019ea6cf-d0b8-734c-9e9d-eb30e2ae6b3d" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MaximumUnsecuredLeverageRatio_019ea6cf-d0b8-75e5-81cf-fb5c982416dc" xlink:href="aat-20260630.xsd#aat_MaximumUnsecuredLeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MaximumUnsecuredLeverageRatio_019ea6cf-d0b8-75e5-81cf-fb5c982416dc" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MaximumRecourseIndebtednessOfTotalAssetValue_019ea6cf-d0b8-703e-a397-69c0b79d30b7" xlink:href="aat-20260630.xsd#aat_MaximumRecourseIndebtednessOfTotalAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ea6ce-8630-7db6-9f0a-b7814cb549a9" xlink:to="loc_aat_MaximumRecourseIndebtednessOfTotalAssetValue_019ea6cf-d0b8-703e-a397-69c0b79d30b7" xlink:type="arc" order="27"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/DEBTSummaryofTotalSecuredNotesPayableOutstandingDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#DEBTSummaryofTotalSecuredNotesPayableOutstandingDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/DEBTSummaryofTotalSecuredNotesPayableOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e2887-153b-7761-aa8b-bfcbaad9c156" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_DebtInstrumentTable_019e2887-153b-7761-aa8b-bfcbaad9c156" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7dbb-bd97-f3e5c5c88184" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-7761-aa8b-bfcbaad9c156" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7dbb-bd97-f3e5c5c88184" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7dbb-bd97-f3e5c5c88184_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7dbb-bd97-f3e5c5c88184" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7dbb-bd97-f3e5c5c88184_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7c67-8bb5-0c2e1065ea8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7dbb-bd97-f3e5c5c88184" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7c67-8bb5-0c2e1065ea8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A508CityCenterBellevueOctober2027Member_019e2887-153b-74b8-854d-898de1ea1ac1" xlink:href="aat-20260630.xsd#aat_A508CityCenterBellevueOctober2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7c67-8bb5-0c2e1065ea8d" xlink:to="loc_aat_A508CityCenterBellevueOctober2027Member_019e2887-153b-74b8-854d-898de1ea1ac1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7d36-9914-6caa4497a374" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-7761-aa8b-bfcbaad9c156" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7d36-9914-6caa4497a374" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7d36-9914-6caa4497a374_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7d36-9914-6caa4497a374" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7d36-9914-6caa4497a374_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-72a6-b183-8fc5933cd42d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7d36-9914-6caa4497a374" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-72a6-b183-8fc5933cd42d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e2887-153b-7fa0-b35e-35afb1830797" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-72a6-b183-8fc5933cd42d" xlink:to="loc_us-gaap_SecuredDebtMember_019e2887-153b-7fa0-b35e-35afb1830797" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-7b54-84b8-1b8980b4f249" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-7761-aa8b-bfcbaad9c156" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-7b54-84b8-1b8980b4f249" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7b54-84b8-1b8980b4f249_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7b54-84b8-1b8980b4f249" xlink:to="loc_dei_EntityDomain_019e2887-153b-7b54-84b8-1b8980b4f249_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7e3c-933a-6323c276b7e8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7b54-84b8-1b8980b4f249" xlink:to="loc_dei_EntityDomain_019e2887-153b-7e3c-933a-6323c276b7e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-778f-bae3-1492bdffff87" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-7e3c-933a-6323c276b7e8" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-778f-bae3-1492bdffff87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019e2887-153b-7eaa-9c82-8f8b13cc368f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019e2887-153b-7eaa-9c82-8f8b13cc368f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-78a8-b253-664fceaa2d69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-78a8-b253-664fceaa2d69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e2887-153b-7782-9394-831e7f6ae0ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_LongTermDebt_019e2887-153b-7782-9394-831e7f6ae0ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2887-153b-70bb-9533-b386988ae799" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2887-153b-70bb-9533-b386988ae799" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-78da-aaa5-aeb38e5f417f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7e1d-b4ce-18833060ae08" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-78da-aaa5-aeb38e5f417f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/DEBTSummaryofTotalUnsecuredNotesPayableOutstandingDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#DEBTSummaryofTotalUnsecuredNotesPayableOutstandingDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/DEBTSummaryofTotalUnsecuredNotesPayableOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-70de-b584-803888d66ec7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-70de-b584-803888d66ec7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-70de-b584-803888d66ec7_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-70de-b584-803888d66ec7" xlink:to="loc_dei_EntityDomain_019e2887-153b-70de-b584-803888d66ec7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-70d2-b32a-3d2e02ad8d6b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-70de-b584-803888d66ec7" xlink:to="loc_dei_EntityDomain_019e2887-153b-70d2-b32a-3d2e02ad8d6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-73f9-9276-b579bcfb6ea7" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-70d2-b32a-3d2e02ad8d6b" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-73f9-9276-b579bcfb6ea7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7f24-b90b-1d5fde70de57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7f24-b90b-1d5fde70de57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7f24-b90b-1d5fde70de57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7f24-b90b-1d5fde70de57" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7f24-b90b-1d5fde70de57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7e34-9407-8b401f22ec2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-7f24-b90b-1d5fde70de57" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7e34-9407-8b401f22ec2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019e2887-153b-7f5a-bdee-c17f6906c432" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7e34-9407-8b401f22ec2f" xlink:to="loc_us-gaap_UnsecuredDebtMember_019e2887-153b-7f5a-bdee-c17f6906c432" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7a68-8f6a-b095bd9c3aa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7a68-8f6a-b095bd9c3aa1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7a68-8f6a-b095bd9c3aa1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7a68-8f6a-b095bd9c3aa1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-7a68-8f6a-b095bd9c3aa1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e2887-153b-7a68-8f6a-b095bd9c3aa1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_TermLoanAMember_019e2887-153b-79fa-902c-921c3e3629eb" xlink:href="aat-20260630.xsd#aat_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_TermLoanAMember_019e2887-153b-79fa-902c-921c3e3629eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesDMember_019e2887-153b-7da3-81c7-5ddb9076b732" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesDMember_019e2887-153b-7da3-81c7-5ddb9076b732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesEMember_019e2887-153b-7ba8-84d2-09de785fd81c" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesEMember_019e2887-153b-7ba8-84d2-09de785fd81c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SeniorGuaranteedNotesSeriesGMember_019e2887-153b-7089-b883-37a8ac980e39" xlink:href="aat-20260630.xsd#aat_SeniorGuaranteedNotesSeriesGMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_SeniorGuaranteedNotesSeriesGMember_019e2887-153b-7089-b883-37a8ac980e39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A3375SeniorUnsecuredNotesMember_019e2887-153b-7693-932f-a93a72ab7ac9" xlink:href="aat-20260630.xsd#aat_A3375SeniorUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_A3375SeniorUnsecuredNotesMember_019e2887-153b-7693-932f-a93a72ab7ac9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_A6.150SeniorUnsecuredNotesMember_019e2887-153b-7328-8885-03ec9c496280" xlink:href="aat-20260630.xsd#aat_A6.150SeniorUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2887-153b-792a-a948-185a717c0ddf" xlink:to="loc_aat_A6.150SeniorUnsecuredNotesMember_019e2887-153b-7328-8885-03ec9c496280" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-7e7e-8e39-39b48b147293" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2887-153b-78a5-8bcc-52de3b6e8724" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-7e7e-8e39-39b48b147293" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7e7e-8e39-39b48b147293_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-7e7e-8e39-39b48b147293" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7e7e-8e39-39b48b147293_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7197-a0c0-135321e863d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019e2887-153b-7e7e-8e39-39b48b147293" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7197-a0c0-135321e863d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019e2887-153b-77d0-866b-fd092fe53c36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7197-a0c0-135321e863d8" xlink:to="loc_us-gaap_InterestRateSwapMember_019e2887-153b-77d0-866b-fd092fe53c36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryLockMember_019e2887-153b-72ff-9879-4837129bc505" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019e2887-153b-7197-a0c0-135321e863d8" xlink:to="loc_us-gaap_TreasuryLockMember_019e2887-153b-72ff-9879-4837129bc505" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2887-153b-7e5e-8a60-b0da1c9d345c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2887-153b-7e5e-8a60-b0da1c9d345c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-751a-9b63-bce07e7bcba7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_019e2887-153b-751a-9b63-bce07e7bcba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019e2887-153b-7ab3-964e-c8e02e737ef4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019e2887-153b-7ab3-964e-c8e02e737ef4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-784f-b783-8377a9ef4130" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-784f-b783-8377a9ef4130" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e2887-153b-74a2-98a3-4a99d55c0871" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_LongTermDebt_019e2887-153b-74a2-98a3-4a99d55c0871" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfInterestRateDerivativesHeld_019e2887-153b-78cd-96fe-591b4025fac3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfInterestRateDerivativesHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_NumberOfInterestRateDerivativesHeld_019e2887-153b-78cd-96fe-591b4025fac3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_019e2887-153b-7ae6-b05a-5cc448d1472b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_019e2887-153b-7ae6-b05a-5cc448d1472b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentExtensionOptions_019e2887-153b-78fc-9a0a-3b1335838966" xlink:href="aat-20260630.xsd#aat_DebtInstrumentExtensionOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_aat_DebtInstrumentExtensionOptions_019e2887-153b-78fc-9a0a-3b1335838966" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_DebtInstrumentExtensionTerm_019e2887-153b-7ca5-934f-eda73514218d" xlink:href="aat-20260630.xsd#aat_DebtInstrumentExtensionTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_aat_DebtInstrumentExtensionTerm_019e2887-153b-7ca5-934f-eda73514218d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainOnDerivative_019e2887-153b-754f-a58b-989ffb8d0540" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainOnDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DerivativeGainOnDerivative_019e2887-153b-754f-a58b-989ffb8d0540" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019e2887-153b-7469-9f6f-52c26e497087" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019e2887-153b-7469-9f6f-52c26e497087" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019e2887-153b-70f0-974e-f6677b6d7f7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019e2887-153b-70f0-974e-f6677b6d7f7a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLossOnDerivative_019e2887-153b-7fca-862c-cfa68d49504e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLossOnDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2887-153b-7c06-a2fa-4685eeda44a8" xlink:to="loc_us-gaap_DerivativeLossOnDerivative_019e2887-153b-7fca-862c-cfa68d49504e" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/PARTNERSCAPITALOFAMERICANASSETSTRUSTLPDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#PARTNERSCAPITALOFAMERICANASSETSTRUSTLPDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/PARTNERSCAPITALOFAMERICANASSETSTRUSTLPDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalUnitLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCapitalUnitsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-7ea8-ab07-ea3b6992e7bf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-7ea8-ab07-ea3b6992e7bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7ea8-ab07-ea3b6992e7bf_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7ea8-ab07-ea3b6992e7bf" xlink:to="loc_dei_EntityDomain_019e2887-153b-7ea8-ab07-ea3b6992e7bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-71d0-b1f0-1beaa04b6e5f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7ea8-ab07-ea3b6992e7bf" xlink:to="loc_dei_EntityDomain_019e2887-153b-71d0-b1f0-1beaa04b6e5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-7842-bb12-1dcb24331160" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-71d0-b1f0-1beaa04b6e5f" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-7842-bb12-1dcb24331160" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019e2887-153b-7ac2-8afc-077f4c835808" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:to="loc_srt_OwnershipAxis_019e2887-153b-7ac2-8afc-077f4c835808" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019e2887-153b-7ac2-8afc-077f4c835808_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019e2887-153b-7ac2-8afc-077f4c835808" xlink:to="loc_srt_OwnershipDomain_019e2887-153b-7ac2-8afc-077f4c835808_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019e2887-153b-7d93-a72f-119802969e3a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019e2887-153b-7ac2-8afc-077f4c835808" xlink:to="loc_srt_OwnershipDomain_019e2887-153b-7d93-a72f-119802969e3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-7c7b-a470-ca136d9e980c" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019e2887-153b-7d93-a72f-119802969e3a" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-7c7b-a470-ca136d9e980c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-153b-78ba-bcff-9e1e8dbec5e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-153b-78ba-bcff-9e1e8dbec5e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-153b-78ba-bcff-9e1e8dbec5e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-153b-78ba-bcff-9e1e8dbec5e5" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-153b-78ba-bcff-9e1e8dbec5e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-153b-7311-956f-144405c47c90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019e2887-153b-78ba-bcff-9e1e8dbec5e5" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-153b-7311-956f-144405c47c90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnerMember_019e2887-153b-76f7-a716-893319350549" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019e2887-153b-7311-956f-144405c47c90" xlink:to="loc_us-gaap_LimitedPartnerMember_019e2887-153b-76f7-a716-893319350549" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e2887-153b-74b5-b3f5-01bd0db278ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e2887-153b-74b5-b3f5-01bd0db278ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2887-153b-74b5-b3f5-01bd0db278ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e2887-153b-74b5-b3f5-01bd0db278ab" xlink:to="loc_us-gaap_EquityComponentDomain_019e2887-153b-74b5-b3f5-01bd0db278ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2887-153b-7fce-881f-d71f4428fe9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e2887-153b-74b5-b3f5-01bd0db278ab" xlink:to="loc_us-gaap_EquityComponentDomain_019e2887-153b-7fce-881f-d71f4428fe9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e2887-153b-7967-864d-b50fb8b62ded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e2887-153b-7fce-881f-d71f4428fe9f" xlink:to="loc_us-gaap_CommonStockMember_019e2887-153b-7967-864d-b50fb8b62ded" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-750c-a109-866be66c46b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalUnitsTable_019e2887-153b-79e3-9988-9ecd01274a69" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-750c-a109-866be66c46b0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-750c-a109-866be66c46b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-750c-a109-866be66c46b0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-750c-a109-866be66c46b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-74f0-8728-b8e9095c8742" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-750c-a109-866be66c46b0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-74f0-8728-b8e9095c8742" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OperatingPartnershipUnitsMember_019e2887-153b-7eff-823c-08b7e053a49f" xlink:href="aat-20260630.xsd#aat_OperatingPartnershipUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-74f0-8728-b8e9095c8742" xlink:to="loc_aat_OperatingPartnershipUnitsMember_019e2887-153b-7eff-823c-08b7e053a49f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SharesHeldByMinorityInterestInOperatingPartnerships_019e2887-153b-701f-9ac3-b3c276a24cae" xlink:href="aat-20260630.xsd#aat_SharesHeldByMinorityInterestInOperatingPartnerships"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_aat_SharesHeldByMinorityInterestInOperatingPartnerships_019e2887-153b-701f-9ac3-b3c276a24cae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019e2887-153b-7598-9220-b3757cdb5555" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019e2887-153b-7598-9220-b3757cdb5555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PartnersCapitalRedemptionConversionRatio_019e2887-153b-78dc-8991-7a9e171dac52" xlink:href="aat-20260630.xsd#aat_PartnersCapitalRedemptionConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_aat_PartnersCapitalRedemptionConversionRatio_019e2887-153b-78dc-8991-7a9e171dac52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019e2887-153b-751a-91f8-598fcdd79d94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019e2887-153b-751a-91f8-598fcdd79d94" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e2887-153b-774b-b596-30d316180ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitLineItems_019e2887-153b-73be-a04f-ffb6bf03a613" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e2887-153b-774b-b596-30d316180ef1" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCNarrativeDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#EQUITYOFAMERICANASSETSTRUSTINCNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:href="aat-20260630.xsd#aat_EquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_EquityTable_019e2887-153b-7394-90cc-277f049f221d" xlink:href="aat-20260630.xsd#aat_EquityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_aat_EquityTable_019e2887-153b-7394-90cc-277f049f221d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019e2887-153b-7c71-a46a-a0a248a59e8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_EquityTable_019e2887-153b-7394-90cc-277f049f221d" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019e2887-153b-7c71-a46a-a0a248a59e8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e2887-153b-7c71-a46a-a0a248a59e8a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019e2887-153b-7c71-a46a-a0a248a59e8a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e2887-153b-7c71-a46a-a0a248a59e8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e2887-153b-724e-a79f-1114246cab76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019e2887-153b-7c71-a46a-a0a248a59e8a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e2887-153b-724e-a79f-1114246cab76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AtMarketEquityProgramMember_019e2887-153b-7eb2-9dfe-b6cda8ed675c" xlink:href="aat-20260630.xsd#aat_AtMarketEquityProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e2887-153b-724e-a79f-1114246cab76" xlink:to="loc_aat_AtMarketEquityProgramMember_019e2887-153b-7eb2-9dfe-b6cda8ed675c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-7e50-8355-a42101cd2467" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_EquityTable_019e2887-153b-7394-90cc-277f049f221d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-7e50-8355-a42101cd2467" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-7e50-8355-a42101cd2467_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-7e50-8355-a42101cd2467" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-7e50-8355-a42101cd2467_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-7511-a738-c0e973ac87c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e2887-153b-7e50-8355-a42101cd2467" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-7511-a738-c0e973ac87c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OperatingPartnershipUnitsMember_019e2887-153b-7be9-bd0b-380cc8f1a4b2" xlink:href="aat-20260630.xsd#aat_OperatingPartnershipUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e2887-153b-7511-a738-c0e973ac87c7" xlink:to="loc_aat_OperatingPartnershipUnitsMember_019e2887-153b-7be9-bd0b-380cc8f1a4b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-7534-915e-5d8d6890ce6e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_EquityTable_019e2887-153b-7394-90cc-277f049f221d" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-7534-915e-5d8d6890ce6e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7534-915e-5d8d6890ce6e_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7534-915e-5d8d6890ce6e" xlink:to="loc_dei_EntityDomain_019e2887-153b-7534-915e-5d8d6890ce6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7a7a-8b52-f9c22053a36e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7534-915e-5d8d6890ce6e" xlink:to="loc_dei_EntityDomain_019e2887-153b-7a7a-8b52-f9c22053a36e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-75e8-85d4-a4282557cc5d" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-7a7a-8b52-f9c22053a36e" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-75e8-85d4-a4282557cc5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_NumberOfSalesAgents_019e2887-153b-7a39-9aec-69f49ebeed6b" xlink:href="aat-20260630.xsd#aat_NumberOfSalesAgents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_aat_NumberOfSalesAgents_019e2887-153b-7a39-9aec-69f49ebeed6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AggregateOfferingPriceOfCommonShare_019e2887-153b-79d2-9903-a7913105bc2f" xlink:href="aat-20260630.xsd#aat_AggregateOfferingPriceOfCommonShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_aat_AggregateOfferingPriceOfCommonShare_019e2887-153b-79d2-9903-a7913105bc2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019e2887-153b-789c-af07-2240edddb69b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019e2887-153b-789c-af07-2240edddb69b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RemainingCapacityToIssue_019e2887-153b-788e-8f72-e42ae25024e7" xlink:href="aat-20260630.xsd#aat_RemainingCapacityToIssue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_aat_RemainingCapacityToIssue_019e2887-153b-788e-8f72-e42ae25024e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockExpense_019e2887-153b-7dab-a29d-eb1ab8de8448" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_us-gaap_RestrictedStockExpense_019e2887-153b-7dab-a29d-eb1ab8de8448" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e2887-153b-76a0-979f-89048de605e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e2887-153b-76a0-979f-89048de605e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_WeightedAverageUnvestedParticipatingSecuritiesOutstanding_019e2887-153b-782c-b494-ad3de4133482" xlink:href="aat-20260630.xsd#aat_WeightedAverageUnvestedParticipatingSecuritiesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_EquityLineItems_019e2887-153b-78fc-9971-b11be377ef91" xlink:to="loc_aat_WeightedAverageUnvestedParticipatingSecuritiesOutstanding_019e2887-153b-782c-b494-ad3de4133482" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCSummaryofActivityofRestrictedStockAwardsDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#EQUITYOFAMERICANASSETSTRUSTINCSummaryofActivityofRestrictedStockAwardsDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCSummaryofActivityofRestrictedStockAwardsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e2887-153b-74b9-935b-a44a97dafed4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2887-153b-7a66-b91d-c6290a6d0337" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e2887-153b-74b9-935b-a44a97dafed4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2887-153b-7a66-b91d-c6290a6d0337" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e2887-153b-7466-9379-1ed54d152ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2887-153b-7a66-b91d-c6290a6d0337" xlink:to="loc_us-gaap_AwardTypeAxis_019e2887-153b-7466-9379-1ed54d152ef7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e2887-153b-7466-9379-1ed54d152ef7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e2887-153b-7466-9379-1ed54d152ef7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e2887-153b-7466-9379-1ed54d152ef7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e2887-153b-77a8-8143-27625d394822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e2887-153b-7466-9379-1ed54d152ef7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e2887-153b-77a8-8143-27625d394822" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e2887-153b-71ac-82bc-929538665847" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e2887-153b-77a8-8143-27625d394822" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e2887-153b-71ac-82bc-929538665847" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e2887-153b-74b9-935b-a44a97dafed4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e2887-153b-7ccb-8576-a0771b0c0b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e2887-153b-7ccb-8576-a0771b0c0b2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e2887-153b-795c-9b91-f44421d6a33b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e2887-153b-795c-9b91-f44421d6a33b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e2887-153b-7034-9521-9c3fb689b543" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e2887-153b-7034-9521-9c3fb689b543" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e2887-153b-763a-84d9-048d8ed66edc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e2887-153b-7808-be28-fce48c0c97c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e2887-153b-763a-84d9-048d8ed66edc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e2887-153b-7fb6-bcef-88d8f686ed41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e2887-153b-74b9-935b-a44a97dafed4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e2887-153b-7315-b178-c0fff9c034a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e2887-153b-7315-b178-c0fff9c034a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e2887-153b-778e-8a4c-0fcdc972b7c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e2887-153b-778e-8a4c-0fcdc972b7c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e2887-153b-72d1-934d-0fd8f40241dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e2887-153b-72d1-934d-0fd8f40241dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e2887-153b-73e8-81de-3931c0f04825" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e2887-153b-7f9d-b04e-106d213cffc9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e2887-153b-73e8-81de-3931c0f04825" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e2887-153b-773d-a248-ff82df99bd42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#COMMITMENTSANDCONTINGENCIESDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:href="aat-20260630.xsd#aat_CommitmentAndContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:href="aat-20260630.xsd#aat_CommitmentAndContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis_019e2887-153b-757d-9eef-ee2af9337b1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis_019e2887-153b-757d-9eef-ee2af9337b1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-757d-9eef-ee2af9337b1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis_019e2887-153b-757d-9eef-ee2af9337b1a" xlink:to="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-757d-9eef-ee2af9337b1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-70ef-8535-6c22956e9a67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis_019e2887-153b-757d-9eef-ee2af9337b1a" xlink:to="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-70ef-8535-6c22956e9a67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_WaikikiBeachWalkRetailMember_019e2887-153b-7f5d-8dc2-e98e0a4c64b7" xlink:href="aat-20260630.xsd#aat_WaikikiBeachWalkRetailMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-70ef-8535-6c22956e9a67" xlink:to="loc_aat_WaikikiBeachWalkRetailMember_019e2887-153b-7f5d-8dc2-e98e0a4c64b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OutriggerHotelsAndResortsMember_019e2887-153b-78c2-ae58-3d14b24150ba" xlink:href="aat-20260630.xsd#aat_OutriggerHotelsAndResortsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-70ef-8535-6c22956e9a67" xlink:to="loc_aat_OutriggerHotelsAndResortsMember_019e2887-153b-78c2-ae58-3d14b24150ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_WbwHotelLesseeLlcMember_019e2887-153b-7f63-bdf1-0fa328425c45" xlink:href="aat-20260630.xsd#aat_WbwHotelLesseeLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentDomain_019e2887-153b-70ef-8535-6c22956e9a67" xlink:to="loc_aat_WbwHotelLesseeLlcMember_019e2887-153b-7f63-bdf1-0fa328425c45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e2887-153b-7700-ae24-9c79234fc7b4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_srt_RangeAxis_019e2887-153b-7700-ae24-9c79234fc7b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-153b-7700-ae24-9c79234fc7b4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e2887-153b-7700-ae24-9c79234fc7b4" xlink:to="loc_srt_RangeMember_019e2887-153b-7700-ae24-9c79234fc7b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-153b-71cb-b329-e2065492cfec" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e2887-153b-7700-ae24-9c79234fc7b4" xlink:to="loc_srt_RangeMember_019e2887-153b-71cb-b329-e2065492cfec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e2887-153b-7cce-ac3c-51ce458317cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e2887-153b-71cb-b329-e2065492cfec" xlink:to="loc_srt_MaximumMember_019e2887-153b-7cce-ac3c-51ce458317cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e2887-153b-7d7b-a8a8-7b21b9328d12" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_srt_StatementGeographicalAxis_019e2887-153b-7d7b-a8a8-7b21b9328d12" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e2887-153b-7d7b-a8a8-7b21b9328d12_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019e2887-153b-7d7b-a8a8-7b21b9328d12" xlink:to="loc_srt_SegmentGeographicalDomain_019e2887-153b-7d7b-a8a8-7b21b9328d12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e2887-153b-7663-889d-6d84db254098" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019e2887-153b-7d7b-a8a8-7b21b9328d12" xlink:to="loc_srt_SegmentGeographicalDomain_019e2887-153b-7663-889d-6d84db254098" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_SouthernCaliforniaMember_019e2887-153b-7be5-9274-cfbae045ef4a" xlink:href="aat-20260630.xsd#aat_SouthernCaliforniaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e2887-153b-7663-889d-6d84db254098" xlink:to="loc_aat_SouthernCaliforniaMember_019e2887-153b-7be5-9274-cfbae045ef4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e2887-153b-76d8-be9f-f25b5a19740f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e2887-153b-76d8-be9f-f25b5a19740f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e2887-153b-76d8-be9f-f25b5a19740f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e2887-153b-76d8-be9f-f25b5a19740f" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e2887-153b-76d8-be9f-f25b5a19740f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e2887-153b-7239-a832-f7c531230555" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e2887-153b-76d8-be9f-f25b5a19740f" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e2887-153b-7239-a832-f7c531230555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019e2887-153b-7bbb-9532-29c577a17bac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e2887-153b-7239-a832-f7c531230555" xlink:to="loc_us-gaap_SalesRevenueNetMember_019e2887-153b-7bbb-9532-29c577a17bac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e2887-153b-7a48-ad6a-5105316addb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e2887-153b-7a48-ad6a-5105316addb8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-7a48-ad6a-5105316addb8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e2887-153b-7a48-ad6a-5105316addb8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-7a48-ad6a-5105316addb8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-75da-b748-5f5f0e7ecca8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e2887-153b-7a48-ad6a-5105316addb8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-75da-b748-5f5f0e7ecca8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019e2887-153b-7598-afa9-f5a34dcfb106" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-75da-b748-5f5f0e7ecca8" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019e2887-153b-7598-afa9-f5a34dcfb106" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019e2887-153b-7285-93f3-529149114628" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e2887-153b-75da-b748-5f5f0e7ecca8" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019e2887-153b-7285-93f3-529149114628" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e2887-153b-70aa-915f-1e696f4a191b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_CommitmentAndContingenciesTable_019e2887-153b-753a-9e06-9b26ee973278" xlink:to="loc_srt_MajorCustomersAxis_019e2887-153b-70aa-915f-1e696f4a191b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e2887-153b-70aa-915f-1e696f4a191b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019e2887-153b-70aa-915f-1e696f4a191b" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e2887-153b-70aa-915f-1e696f4a191b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e2887-153b-7b1e-9351-e1acf146b21d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019e2887-153b-70aa-915f-1e696f4a191b" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e2887-153b-7b1e-9351-e1acf146b21d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RetailTenantMember_019e2887-153b-733e-b6eb-6632ee83c8a3" xlink:href="aat-20260630.xsd#aat_RetailTenantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e2887-153b-7b1e-9351-e1acf146b21d" xlink:to="loc_aat_RetailTenantMember_019e2887-153b-733e-b6eb-6632ee83c8a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyManagementFeePercentFee_019e2887-153b-77b3-a76b-25f80ed93466" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyManagementFeePercentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_us-gaap_PropertyManagementFeePercentFee_019e2887-153b-77b3-a76b-25f80ed93466" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_CalendarMonths_019e2887-153b-7aca-9201-3b21017d353b" xlink:href="aat-20260630.xsd#aat_CalendarMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_CalendarMonths_019e2887-153b-7aca-9201-3b21017d353b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MaximumPercentageOfHotelsFiscalYearGrossRevenuesPaidForAggregateYearlyManagementFee_019e2887-153b-7206-92b3-8f4716afe855" xlink:href="aat-20260630.xsd#aat_MaximumPercentageOfHotelsFiscalYearGrossRevenuesPaidForAggregateYearlyManagementFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_MaximumPercentageOfHotelsFiscalYearGrossRevenuesPaidForAggregateYearlyManagementFee_019e2887-153b-7206-92b3-8f4716afe855" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PropertyManagementFeeMonthlyFee_019e2887-153b-7776-957a-983fba1d69a4" xlink:href="aat-20260630.xsd#aat_PropertyManagementFeeMonthlyFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_PropertyManagementFeeMonthlyFee_019e2887-153b-7776-957a-983fba1d69a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_TerminationNoticePeriod_019e2887-153b-7967-96d4-3810a224c4bc" xlink:href="aat-20260630.xsd#aat_TerminationNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_TerminationNoticePeriod_019e2887-153b-7967-96d4-3810a224c4bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_YearsOfContract_019e2887-153b-7821-a28c-957d001d3ce4" xlink:href="aat-20260630.xsd#aat_YearsOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_YearsOfContract_019e2887-153b-7821-a28c-957d001d3ce4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PercentageOfHotelOccupancyGrossRevenuePaidForFranchiseRoyaltyFee_019e2887-153b-7d0c-bf8f-5886182be59d" xlink:href="aat-20260630.xsd#aat_PercentageOfHotelOccupancyGrossRevenuePaidForFranchiseRoyaltyFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_PercentageOfHotelOccupancyGrossRevenuePaidForFranchiseRoyaltyFee_019e2887-153b-7d0c-bf8f-5886182be59d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PercentageOfHotelOccupancyGrossRevenuePaidForProgramFee_019e2887-153b-7ade-9398-76df54ec144b" xlink:href="aat-20260630.xsd#aat_PercentageOfHotelOccupancyGrossRevenuePaidForProgramFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_PercentageOfHotelOccupancyGrossRevenuePaidForProgramFee_019e2887-153b-7ade-9398-76df54ec144b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossOnContractTerminationForDefault_019e2887-153b-7a89-8986-065093b6a4af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossOnContractTerminationForDefault"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_us-gaap_LossOnContractTerminationForDefault_019e2887-153b-7a89-8986-065093b6a4af" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_NumberOfConsolidatedProperties_019e2887-153b-7182-b101-a7fd987c51db" xlink:href="aat-20260630.xsd#aat_NumberOfConsolidatedProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_aat_NumberOfConsolidatedProperties_019e2887-153b-7182-b101-a7fd987c51db" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e2887-153b-70df-a60b-24156fc24c62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_CommitmentAndContingenciesLineItems_019e2887-153b-7090-ae24-9fcc83cd68f3" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e2887-153b-70df-a60b-24156fc24c62" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/LEASESNarrativeDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#LEASESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/LEASESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionLineItems_019e2887-153b-7c28-a208-68cf86fbfa76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionTable_019e2887-153b-75ab-9ba2-691851bb8a42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019e2887-153b-7c28-a208-68cf86fbfa76" xlink:to="loc_us-gaap_LessorLeaseDescriptionTable_019e2887-153b-75ab-9ba2-691851bb8a42" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e2887-153b-7ddf-8ce0-d242e37d2a05" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LessorLeaseDescriptionTable_019e2887-153b-75ab-9ba2-691851bb8a42" xlink:to="loc_srt_RangeAxis_019e2887-153b-7ddf-8ce0-d242e37d2a05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-153b-7ddf-8ce0-d242e37d2a05_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e2887-153b-7ddf-8ce0-d242e37d2a05" xlink:to="loc_srt_RangeMember_019e2887-153b-7ddf-8ce0-d242e37d2a05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2887-153b-7dbe-a914-6bc215a2eb9f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e2887-153b-7ddf-8ce0-d242e37d2a05" xlink:to="loc_srt_RangeMember_019e2887-153b-7dbe-a914-6bc215a2eb9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e2887-153b-7340-9e85-d982aa09cb97" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e2887-153b-7dbe-a914-6bc215a2eb9f" xlink:to="loc_srt_MinimumMember_019e2887-153b-7340-9e85-d982aa09cb97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e2887-153b-71da-a5a7-d934e84f8ac1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e2887-153b-7dbe-a914-6bc215a2eb9f" xlink:to="loc_srt_MaximumMember_019e2887-153b-71da-a5a7-d934e84f8ac1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019eb60a-85d8-7fc8-84e2-8118aff47e1b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LessorLeaseDescriptionTable_019e2887-153b-75ab-9ba2-691851bb8a42" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019eb60a-85d8-7fc8-84e2-8118aff47e1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019eb60a-85d8-7fc8-84e2-8118aff47e1b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019eb60a-85d8-7fc8-84e2-8118aff47e1b" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019eb60a-85d8-7fc8-84e2-8118aff47e1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019eb60a-85d8-7ce8-b489-523925c6d761" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019eb60a-85d8-7fc8-84e2-8118aff47e1b" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019eb60a-85d8-7ce8-b489-523925c6d761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ApartmentBuildingMember_019eb60a-c556-7068-ab94-b15ada52de4f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ApartmentBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019eb60a-85d8-7ce8-b489-523925c6d761" xlink:to="loc_srt_ApartmentBuildingMember_019eb60a-c556-7068-ab94-b15ada52de4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseTermOfContract_019e2887-153b-729a-9b52-951ed2c7896a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019e2887-153b-7c28-a208-68cf86fbfa76" xlink:to="loc_us-gaap_LessorOperatingLeaseTermOfContract_019e2887-153b-729a-9b52-951ed2c7896a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_LeaseExtensionOptionExercisePeriod_019e2887-153b-7889-b434-5a974802e81f" xlink:href="aat-20260630.xsd#aat_LeaseExtensionOptionExercisePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019e2887-153b-7c28-a208-68cf86fbfa76" xlink:to="loc_aat_LeaseExtensionOptionExercisePeriod_019e2887-153b-7889-b434-5a974802e81f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2887-153b-742d-b1a5-18a8b636bb63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019e2887-153b-7c28-a208-68cf86fbfa76" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2887-153b-742d-b1a5-18a8b636bb63" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSESummaryofPrincipalComponentsofRentalIncomeDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#COMPONENTSOFRENTALINCOMEANDEXPENSESummaryofPrincipalComponentsofRentalIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSESummaryofPrincipalComponentsofRentalIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:href="aat-20260630.xsd#aat_RentalIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RentalIncomeTable_019e2887-153b-7d59-8234-735b5140efe9" xlink:href="aat-20260630.xsd#aat_RentalIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_aat_RentalIncomeTable_019e2887-153b-7d59-8234-735b5140efe9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7c1d-8a2e-b10e04c7ab01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_aat_RentalIncomeTable_019e2887-153b-7d59-8234-735b5140efe9" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7c1d-8a2e-b10e04c7ab01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-7c1d-8a2e-b10e04c7ab01_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7c1d-8a2e-b10e04c7ab01" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-7c1d-8a2e-b10e04c7ab01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7c1d-8a2e-b10e04c7ab01" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OfficeSegmentMember_019e2887-153b-775e-a4c8-3294b756cc95" xlink:href="aat-20260630.xsd#aat_OfficeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:to="loc_aat_OfficeSegmentMember_019e2887-153b-775e-a4c8-3294b756cc95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RetailSegmentMember_019e2887-153b-7755-9ddf-dc1314807b6d" xlink:href="aat-20260630.xsd#aat_RetailSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:to="loc_aat_RetailSegmentMember_019e2887-153b-7755-9ddf-dc1314807b6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MultifamilySegmentMember_019e2887-153b-7f6c-a40e-7bfca975c37a" xlink:href="aat-20260630.xsd#aat_MultifamilySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:to="loc_aat_MultifamilySegmentMember_019e2887-153b-7f6c-a40e-7bfca975c37a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MixedUseSegmentMember_019e2887-153b-7fc5-806c-1f98c553d88b" xlink:href="aat-20260630.xsd#aat_MixedUseSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a9f-857d-e3ed6749fd23" xlink:to="loc_aat_MixedUseSegmentMember_019e2887-153b-7fc5-806c-1f98c553d88b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_LeaseRentalIncome_019e2887-153b-7e69-a486-2313938d8c37" xlink:href="aat-20260630.xsd#aat_LeaseRentalIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_aat_LeaseRentalIncome_019e2887-153b-7e69-a486-2313938d8c37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_LeaseRentalIncomePercentRent_019e2887-153b-70a9-b259-f73c0dd8017f" xlink:href="aat-20260630.xsd#aat_LeaseRentalIncomePercentRent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_aat_LeaseRentalIncomePercentRent_019e2887-153b-70a9-b259-f73c0dd8017f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2887-153b-77dc-8c31-fc61184af31a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2887-153b-77dc-8c31-fc61184af31a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OtherRealEstateRentalRevenue_019e2887-153b-792e-88f6-69eb5879d92a" xlink:href="aat-20260630.xsd#aat_OtherRealEstateRentalRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_aat_OtherRealEstateRentalRevenue_019e2887-153b-792e-88f6-69eb5879d92a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-153b-775a-8bed-68df13115039" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aat_RentalIncomeLineItems_019e2887-153b-7f13-98fb-d14046aa9533" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-153b-775a-8bed-68df13115039" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/RELATEDPARTYTRANSACTIONSDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#RELATEDPARTYTRANSACTIONSDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/RELATEDPARTYTRANSACTIONSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e2887-153b-7e98-85e5-37fb3d8b26d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e2887-153b-7e98-85e5-37fb3d8b26d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e2887-153b-7b00-8fbc-77ca5406c113" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e2887-153b-7e98-85e5-37fb3d8b26d3" xlink:to="loc_srt_CounterpartyNameAxis_019e2887-153b-7b00-8fbc-77ca5406c113" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7b00-8fbc-77ca5406c113_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019e2887-153b-7b00-8fbc-77ca5406c113" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7b00-8fbc-77ca5406c113_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7fea-8155-652b3dec41f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019e2887-153b-7b00-8fbc-77ca5406c113" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7fea-8155-652b3dec41f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsInc.Member_019e2887-153b-7144-92b2-d60f8b996d8b" xlink:href="aat-20260630.xsd#aat_AmericanAssetsInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7fea-8155-652b3dec41f2" xlink:to="loc_aat_AmericanAssetsInc.Member_019e2887-153b-7144-92b2-d60f8b996d8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_WBWCHPLLCMember_019e2887-153b-758b-96cd-a1b9b67e2ec5" xlink:href="aat-20260630.xsd#aat_WBWCHPLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e2887-153b-7fea-8155-652b3dec41f2" xlink:to="loc_aat_WBWCHPLLCMember_019e2887-153b-758b-96cd-a1b9b67e2ec5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e2887-153b-7ddf-9a71-7436d5c2f94b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e2887-153b-7e98-85e5-37fb3d8b26d3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e2887-153b-7ddf-9a71-7436d5c2f94b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e2887-153b-7ddf-9a71-7436d5c2f94b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e2887-153b-7ddf-9a71-7436d5c2f94b" xlink:to="loc_us-gaap_RelatedPartyDomain_019e2887-153b-7ddf-9a71-7436d5c2f94b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e2887-153b-77e9-b1b1-1f2f17fb5417" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e2887-153b-7ddf-9a71-7436d5c2f94b" xlink:to="loc_us-gaap_RelatedPartyDomain_019e2887-153b-77e9-b1b1-1f2f17fb5417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019e2887-153b-766c-9f35-630fabf2e803" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019e2887-153b-77e9-b1b1-1f2f17fb5417" xlink:to="loc_us-gaap_RelatedPartyMember_019e2887-153b-766c-9f35-630fabf2e803" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseTermOfContract_019e2887-153b-7afe-859c-f82e13cfb999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_us-gaap_LessorOperatingLeaseTermOfContract_019e2887-153b-7afe-859c-f82e13cfb999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OperatingLeaseAverageAnnualRent_019e2887-153b-7f97-b07d-5e4bb635086d" xlink:href="aat-20260630.xsd#aat_OperatingLeaseAverageAnnualRent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_aat_OperatingLeaseAverageAnnualRent_019e2887-153b-7f97-b07d-5e4bb635086d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-153b-74b0-8258-8d73b9f4ef41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019e2887-153b-74b0-8258-8d73b9f4ef41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PercentageOfInvestmentInRelatedParty_019e2887-153b-7e9e-b740-b41ac6949c62" xlink:href="aat-20260630.xsd#aat_PercentageOfInvestmentInRelatedParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_aat_PercentageOfInvestmentInRelatedParty_019e2887-153b-7e9e-b740-b41ac6949c62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-153b-73bb-8ab4-47ed2eaf2475" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfOtherPropertyOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e2887-153b-730f-9894-ce0af3154351" xlink:to="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-153b-73bb-8ab4-47ed2eaf2475" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofSegmentActivityDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#SEGMENTREPORTINGSummaryofSegmentActivityDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofSegmentActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-7086-8c52-c57f6d7f2841" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-7086-8c52-c57f6d7f2841" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7358-a35e-2ad89172e4b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-7086-8c52-c57f6d7f2841" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7358-a35e-2ad89172e4b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-7358-a35e-2ad89172e4b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7358-a35e-2ad89172e4b4" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-7358-a35e-2ad89172e4b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7358-a35e-2ad89172e4b4" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OfficeSegmentMember_019e2887-153b-72a1-bbb9-574036738215" xlink:href="aat-20260630.xsd#aat_OfficeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:to="loc_aat_OfficeSegmentMember_019e2887-153b-72a1-bbb9-574036738215" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RetailSegmentMember_019e2887-153b-77f8-967c-6dd30b4b6c4a" xlink:href="aat-20260630.xsd#aat_RetailSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:to="loc_aat_RetailSegmentMember_019e2887-153b-77f8-967c-6dd30b4b6c4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MultifamilySegmentMember_019e2887-153b-78d6-9138-77a147e00c76" xlink:href="aat-20260630.xsd#aat_MultifamilySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:to="loc_aat_MultifamilySegmentMember_019e2887-153b-78d6-9138-77a147e00c76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MixedUseSegmentMember_019e2887-153b-7b48-810f-56cabadecde3" xlink:href="aat-20260630.xsd#aat_MixedUseSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-78c0-941e-29273dd74aa6" xlink:to="loc_aat_MixedUseSegmentMember_019e2887-153b-7b48-810f-56cabadecde3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019e2887-153b-7d11-81ed-04b3f24b7160" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019e2887-153b-7d11-81ed-04b3f24b7160" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-153b-7d77-aa37-f37d02ac917d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfOtherPropertyOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_CostOfOtherPropertyOperatingExpense_019e2887-153b-7d77-aa37-f37d02ac917d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateTaxExpense_019e2887-153b-71a8-8f6d-411a2f71a15c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateTaxExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_RealEstateTaxExpense_019e2887-153b-71a8-8f6d-411a2f71a15c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_PropertyExpenses_019e2887-153b-7487-a455-15086aa13cbe" xlink:href="aat-20260630.xsd#aat_PropertyExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_aat_PropertyExpenses_019e2887-153b-7487-a455-15086aa13cbe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e2887-153b-72e4-9d8c-35d8284af6b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e2887-153b-72e4-9d8c-35d8284af6b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019e2887-153b-7eda-8025-8b54b0a43068" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7901-a80f-483dcece51e8" xlink:to="loc_us-gaap_GrossProfit_019e2887-153b-7eda-8025-8b54b0a43068" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofNetRealEstateandSecuredNotePayableBalancesforEachSegmentDetails" xlink:type="simple" xlink:href="aat-20260630.xsd#SEGMENTREPORTINGSummaryofNetRealEstateandSecuredNotePayableBalancesforEachSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofNetRealEstateandSecuredNotePayableBalancesforEachSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-79ba-9ee5-07a9f9071032" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-79ba-9ee5-07a9f9071032" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-70b0-a1f1-5f7b548d0a2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-79ba-9ee5-07a9f9071032" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-70b0-a1f1-5f7b548d0a2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-70b0-a1f1-5f7b548d0a2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-70b0-a1f1-5f7b548d0a2e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-70b0-a1f1-5f7b548d0a2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7dc1-b237-3eccd81334ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e2887-153b-70b0-a1f1-5f7b548d0a2e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7dc1-b237-3eccd81334ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e2887-153b-76ac-8a77-1704fbdc16e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2887-153b-7dc1-b237-3eccd81334ff" xlink:to="loc_us-gaap_SecuredDebtMember_019e2887-153b-76ac-8a77-1704fbdc16e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e2887-153b-7c70-938e-336f0a45410c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-79ba-9ee5-07a9f9071032" xlink:to="loc_dei_LegalEntityAxis_019e2887-153b-7c70-938e-336f0a45410c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-7c70-938e-336f0a45410c_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7c70-938e-336f0a45410c" xlink:to="loc_dei_EntityDomain_019e2887-153b-7c70-938e-336f0a45410c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e2887-153b-76bf-b0f1-7a90d583b28a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e2887-153b-7c70-938e-336f0a45410c" xlink:to="loc_dei_EntityDomain_019e2887-153b-76bf-b0f1-7a90d583b28a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-73ce-8dd4-f8094ab0b122" xlink:href="aat-20260630.xsd#aat_AmericanAssetsTrustL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e2887-153b-76bf-b0f1-7a90d583b28a" xlink:to="loc_aat_AmericanAssetsTrustL.P.Member_019e2887-153b-73ce-8dd4-f8094ab0b122" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7e67-93ce-ee5dee0008e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e2887-153b-79ba-9ee5-07a9f9071032" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7e67-93ce-ee5dee0008e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-7e67-93ce-ee5dee0008e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7e67-93ce-ee5dee0008e1" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-7e67-93ce-ee5dee0008e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e2887-153b-7e67-93ce-ee5dee0008e1" xlink:to="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_OfficeSegmentMember_019e2887-153b-7382-bbd3-5f83cd3075af" xlink:href="aat-20260630.xsd#aat_OfficeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:to="loc_aat_OfficeSegmentMember_019e2887-153b-7382-bbd3-5f83cd3075af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_RetailSegmentMember_019e2887-153b-764a-b09b-669522d3fa42" xlink:href="aat-20260630.xsd#aat_RetailSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:to="loc_aat_RetailSegmentMember_019e2887-153b-764a-b09b-669522d3fa42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MultifamilySegmentMember_019e2887-153b-74a5-ae37-d98b7b3106e4" xlink:href="aat-20260630.xsd#aat_MultifamilySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:to="loc_aat_MultifamilySegmentMember_019e2887-153b-74a5-ae37-d98b7b3106e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aat_MixedUseSegmentMember_019e2887-153b-7603-9644-bc08ccfa3d70" xlink:href="aat-20260630.xsd#aat_MixedUseSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e2887-153b-7a5d-ae8e-e4bcaefb8476" xlink:to="loc_aat_MixedUseSegmentMember_019e2887-153b-7603-9644-bc08ccfa3d70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNet_019e2887-153b-7210-93b3-66a17874e31d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNet_019e2887-153b-7210-93b3-66a17874e31d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019e2887-153b-75c7-b864-c1086dfc72f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:to="loc_us-gaap_NotesPayable_019e2887-153b-75c7-b864-c1086dfc72f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-7946-9195-9c776f3b4c7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019e2887-153b-7946-9195-9c776f3b4c7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e2887-153b-7d69-9e94-3b764f260e76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e2887-153b-7631-949e-642f5acb1c6e" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e2887-153b-7d69-9e94-3b764f260e76" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
