The　inert　surface　of　extruded　polystyrene　foams　(XPSF)　was　activated　by　ultraviolet-ozone　(UVO)　for　the　first　time　to　improve　the　interfacial　compatibility　with　mortar.　From　the　structural　analysis　(X-ray　photoelectron　spectroscopic　(XPS)　and　contact　angle　(CA)),　it　was　suggested　that　a　10　min　UVO　exposure　was　efficient　enough　to　introduce　oxygen-contained　elements　(such　as　carboxyl　groups)　upon　the　obtained　UVO-XPSF　surface,　leading　to　the　increased　bonding　strength　(BS)　from　0.058　MPa　of　neat　XPSF/mortar　composites　to　0.088　MPa.　Then,　3aminopropyl　triethoxysilane　(APTES)　was　selected　as　the　promoter　to　further　enhance　the　BS　value　of　XPSF/　mortar　composites.　The　presence　of　the　silane　was　confirmed　by　CA,　Fourier　transform　infrared-attenuated　total　reflection　(FTIR-ATR)　and　XPS.　By　optimizing　the　reaction　conditions　(activation　and　reaction　time:　7　and　3　min,　concentration　of　APTES:　2%　and　pH　value　of　the　silane　solution:　10),　a　maximum　BS　of　0.168　MPa　could　be　obtained.　Through　the　mechanism　analysis,　it　was　demonstrated　that　APTES　acted　as　a　chemical　bridge　that　covalently　jointed　XPSF　by　the　formation　of　amide　peptide　and　inorganic　mortar　by　the　condensation　of　silanols.