Nowadays,　seismic　isolation　system　has　been　widely　applied　in　the　world　to　mitigate　damage　risk　of　structures.　Although　maximum　displacement　demand　can　be　obtained　through　nonlinear　time　history　(NLTH)　analysis,　many　approximate　methods　are　frequently　recommended　in　structural　specifications　to　reduce　the　required　computational　time.　One　of　the　best-known　methods　is　the　equivalent　linear　(EL)　method,　in　which　the　nonlinear　response　of　isolator　can　be　adequately　modeled　using　a　fictitious　viscously　damped　elastic　structure.　In　this　paper,　a　comparison　between　existing　expressions　supplying　the　state　of　research　is　carried　out　and　then,　an　improved　expression　is　presented　for　equivalent　linearization　of　structures　supported　on　lead　rubber　bearings　(LRB).　Based　on　the　concept　of　secant　stiffness,　the　optimal　damping　ratios,　which　minimize　the　errors　of　maximum　displacement　between　EL　analysis　and　NLTH　analysis,　are　calculated　and　averaged　over　12　ground　motions.　Then,　a　rational　model　to　estimate　equivalent　damping　ratio　is　derived　through　statistic　analysis　of　the　optimal　damping　ratios.　To　examine　the　prediction　accuracy　of　the　proposed　model,　mean　ratios　of　approximate　to　exact　maximum　displacement　and　root　mean　square　error　for　different　isolated　period　are　calculated　as　evaluation　indicator.　Compared　with　other　EL　models,　the　newly　proposed　model　predicts　a　displacement　that　is　in　better　agreement　with　the　one　obtained　through　NLTH　analysis.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.