Strong motion records provide the most reliable source of information concerning the dynamic behavior of structures and seismic design technology. This paper presents on-line parameters estimation of effective secant stiffness and equivalent damping ratio using the real-time hysteresis loops which are based on real observation of strong motion of buildings under extreme event. Stiffness deterioration and the change of equivalent damping ratio of four buildings are estimated from BRI Network records. Deteriorating distributed elements (DDE) model is used to simulate time-dependent stiffness deterioration behavior. Time-dependent linear model is used to estimate the change in effective stiffness and damping in time during non-linear deteriorating hysteretic behavior. The Hachinohe City Hall building and a building in Tohoku University that experienced severe earthquake motions were selected in order to verify the proposed model through comparison with the result of non-linear analysis.