Equivalent　linearization　of　seismic　isolation　systems　is　often　recommended　in　modern　structural　specifications　for　the　purpose　of　simplification.　In　this　paper,　limited　conditions　specified　in　equivalent　linearization　of　seismic　isolation　system　are　investigated　when　subjected　to　seismic　loads.　A　large　number　of　numerical　simulations,　including　both　approximate　linear　and　exact　nonlinear　analyses,　are　performed　using　a　program　specially　developed　by　MATLAB　in　conjunction　with　OpenSees.　Approximate　to　exact　maximum　displacement　ratio　averaged　over　seven　earthquake　ground　motions　is　selected　as　the　evaluation　indicator.　Results　reveal　that,　although　satisfactory　estimates　can　be　obtained　if　the　limited　conditions　are　met,　the　application　scope　of　equivalent　linearization　of　seismic　isolation　system　is　significantly　restricted.　To　improve　the　prediction　accuracy　of　equivalent　linear　analysis　in　a　wider　parameter　space,　equivalent　linear　model　recommended　in　codes　is　modified　through　introducing　a　factor,　which　is　related　to　ductility　ratio,　post-to-pre　yield　stiffness　ratio　and　initial　period　of　seismic　isolation　system.　It　is　demonstrated　that　the　newly　proposed　equivalent　linear　model　yields　more　accurate　results　when　compared　with　other　equivalent　linear　models.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.