A　novel　time-domain　identification　technique　is　developed　for　the　seismic　response　analysis　of　soil-structure　interaction.　A　two-degree-of-freedom　(2DOF)　model　with　eight　lumped　parameters　is　adopted　to　model　the　frequency-dependent　behavior　of　soils.　For　layered　soil,　the　equivalent　eight　parameters　of　the　2DOF　model　are　identified　by　the　extended　Kalman　filter　(EKF)　method　using　recorded　seismic　data.　The　polynomial　approximations　for　derivation　of　state　estimators　are　applied　in　the　EKF　procedure.　A　realistic　identification　example　is　given　for　the　layered-soil　of　a　building　site　in　Anchorage,　Alaska　in　the　United　States.　Results　of　the　example　demonstrate　the　feasibility　and　practicality　of　the　proposed　identification　technique.　The　2DOF　soil　model　and　the　identification　technique　can　be　used　for　nonlinear　response　analysis　of　soil-structure　interaction　in　the　time-domain　for　layered　or　complex　soil　conditions.　The　identified　parameters　can　be　stored　in　a　database　for　use　in　other　similar　soil　conditions.　If　a　universal　database　that　covers　information　related　to　most　soil　conditions　is　developed　in　the　future,　engineers　could　conveniently　perform　time　history　analyses　of　soil-structural　interaction.