The　stability　of　pile-supported　structures　under　earthquake　loads　involves　complex　dynamic　soil-structure　interaction　(SSI).　A　series　of　large-scale　shaking　table　experiments　was　performed　to　investigate　the　seismic　performance　and　SSI　of　pile-supported　structures　considering　different　ground　conditions.　Lateral　soil　resistance　and　dynamic　displacements　of　superstructures　located　in　nonliquefiable　and　liquefiable　sites　as　well　as　a　rigid　foundation　were　measured　during　shaking　tests.　The　measured　responses　were　analyzed　to　investigate　the　P-Delta　effect　on　structural　stability.　It　was　observed　that　the　soil　lateral　resistance　to　the　pile　cap　at　the　nonliquefiable　site　was　large　and　represented　the　main　component　of　the　lateral　bearing　capacity　resisting　structure　overturning.　On　the　other　hand,　the　lateral　resistance　of　liquefied　soil　on　piles　was　insignificant　and　the　lateral　bearing　capacity　was　derived　primarily　from　soil　resistance　to　pile　cap.　The　analysis　of　the　measured　dynamic　displacements　demonstrated　that　the　seismic　instability　of　the　structure　was　mainly　due　to　the　P-Delta　effect　caused　by　the　rotation　of　the　foundation,　especially　in　liquefied　sites.　In　addition,　comparison　with　the　results　of　base　shears　and　bending　moments　with　the　rigid　base　assumption　allows　for　an　in-depth　discussion　of　the　effect　of　SSI　on　structural　seismic　design.　(C)　2021　American　Society　of　Civil　Engineers.