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　O-2　and　characterized　by　XRD,　N-2　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-Bi2SiO5/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/N-2=1/4/20cm(3)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　N-2　absorption-desorption　isotherms　reveal　that　a　reasonable　calcination　temperature　is　723K.　The　reaction　mechanism　of　propylene　epoxidation　on　MoO3-Bi2SiO5/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.