MoO3-Bi2SiO5/SiO2　catalysts　with　a　Mo/Bi　molar　ratio　of　5,　prepared　by　a　two-step　hydrothermal　and　simple　impregnation　method,　were　investigated　for　the　epoxidation　of　propylene　by　O2　and　characterized　by　XRD,　N2　absorption-desorption　isotherms,　thermogravimetric　analysis　(TGA),　temperature-programmed　reduction,　NH3　temperature-programmed　desorption　(TPD),　and　IR,　Raman,　and　X-ray　photoelectron　spectroscopy　(XPS).　On　MoO3-Bi2SiO　5/SiO2　with　Mo/Bi=5　calcined　at　723K,　a　propylene　conversion　of　21.99　%　and　a　propylene　oxide　selectivity　of　55.14　%　were　obtained　at　0.15MPa,　673K,　and　flow　rates　of　C3H6/O　2/N2=1/4/20cm3　min-1.　XRD,　IR　spectroscopy,　and　XPS　results　show　that　Bi2SiO5　and　MoO3　are　crystalline　nanoparticles.　NH3-TPD　results　indicate　that　the　surface　acid　sites　are　necessary　for　the　high　catalytic　activity.　The　results　of　TGA　and　N2　absorption-desorption　isotherms　reveal　that　a　reasonable　calcination　temperature　is　723K.　The　reaction　mechanism　of　propylene　epoxidation　on　MoO3-Bi2SiO　5/SiO2　catalysis　is　hypothesized　to　involve　an　allylic　radical　generated　at　the　molybdenum　oxide　species　and　the　activation　of　O　2　at　the　bismuth　oxide　cations.　A　new　sensation　in　epoxidation:　We　describe　the　probable　synergistic　effects　of　MoO3　and　Bi　2SiO5　in　propylene　epoxidation.　The　reactive　centers　consist　of　nanoparticulate　species　of　crystalline　MoO3　to　activate　the　propylene　and　bismuth　oxide　cluster　cations　to　activate　O2.　©　2014　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.