Although　peak　response　of　seismic　isolation　systems　can　be　obtained　through　nonlinear　time　history　analysis　method,　approximate　linear　elastic　analysis　method　is　frequently　proposed　in　recent　structural　codes　to　reduce　the　computational　effort　and　to　simplify　the　design　procedure.　Of　the　approximate　methods,　the　equivalent　linearization　(EL)　method　is　best　known.　In　this　study,　fourteen　EL　methods　proposed　in　the　literatures　are　assessed　based　on　single-degree-of-freedom　(SDOF).　systems　with　bilinear　hysteretic　behavior.　A　large　number　of　numerical　simulations　are　performed　using　a　program　developed　by　MATLAB　in　combination　with　OpenSees　to　evaluate　the　influence　of　ductility　ratio　and　initial　period　on　the　accuracy　of　EL　methods　to　estimate　the　maximum　inelastic　displacement　of　bilinear　SDOF　systems　when　subjected　to　12　earthquake　ground　motions.　A　set　of　20　ductility　ratios　ranging　from　2　to　50　are　considered,　as　well　as　15　initial　natural　periods　between　0.1.　s　and　1.5.　s.　Ratios　of　approximate　to　exact　maximum　displacement　corresponding　to　each　EL　method　are　averaged　over　the　considered　ground　motions,　and　the　standard　deviation　of　investigated　ratios　is　also　calculated　to　measure　the　degree　of　dispersion.　Eventually,　comments　on　the　accuracy　of　different　EL　methods　are　given　to　make　their　applications　more　appropriate　in　practical　design　of　base　isolation　systems.　©　2013　Elsevier　Ltd.