Abstract: In this paper, nonlinear time history analysis of isolated bridges is conducted with the use of large numbers of seismic waves which have same response spectrum and similar envelop in time-domain. It is found that the responses of isolated bridges with lead-rubber bearings differ from each other to a large extent. The maximum response is sensitive to the total process of seismic ground motion. The lead-rubber bearings are a very efficient energy dissipation system. The initial yielding force of lead-rubber bearings has an important influence on isolation effectiveness.