A novel time-domain identification technique is developed for the seismic response analysis of soil-structurc interaction. A two-degree-of-freedom (2DOF) model with eight lumped parameters is adopted to model the frequencydependent 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 arc applied in the EKF procedure. A realistic identification cxamplc 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. Ifa 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.