To obtain seismic response characteristics of high-rise buildings with base isolation system, dynamic response analyses have been conducted using lumped mass model consisting of two masses. In this study, influence of natural period of a superstructure on reduction of lateral seismic force and seismic response drift of isolation interface was examined. As natural period of a superstructure becomes longer, reduction effect of lateral seismic force decreases. But this reduction effect is still more than 50 % for superstructures with natural periods of 3 to 4 seconds. In this case, response drifts of isolation interface are less than response drifts of low-rise or middle hieght buildings.
