Friction　pendulum　system　(FPS)　is　one　of　the　most　effective　base　isolation　systems,　which　is　widely　used　for　seismic　upgrading　of　existing　buildings.　FPS　is　almost　always　non-linear　and　often　strongly　non-linear,　so　a　mechanical　model　of　FPS　bearing　is　of　great　importance　in　seismic　analysis.　In　this　paper,　three　different　models　of　FPS　bearing　are　described　and　a　building　severely　damaged　by　the　L＇Aquila　earthquake　in　2009　is　examined　according　to　the　latest　Italian　code.　Then,　a　case　study　presenting　briefly　an　innovative　technique　that　is　able　to　introduce　base　isolation　on　existing　buildings　is　provided　with　reference　to　the　use　of　FPS.　Different　kinds　of　analyses,　including　response　spectrum　analysis　and　linear　and　non-linear　dynamic　analyses,　are　performed　under　the　life-safety　limit　state.　Storey　shear,　inter-storey　drift,　effective　stiffness　and　energy　dissipation　are　the　considered　parameters　to　investigate　the　effectiveness　of　the　retrofitting　procedure　and　analysis　techniques.