The photo-assisted epoxidation of styrene over V/SBA-15 modified by alkaline-earth metal ions was investigated with hydrogen peroxide at room temperature. The results indicated that the isolated VO4 tetrahedron dispersed on the SiO2 was the photo-assisted catalytic active site for the formation of styrene oxide, while V5+ polymer species in V/SBA-15 with highly loaded V species caused deep oxidation of styrene oxide. Among the catalysts modified by alkaline-earth metal ions, Mg-V/SBA-15 displayed the best catalytic performance. It was probably due to the fact that the metallic character of Mg was weaker in alkaline-earth metals, so it was easier to disperse V5+ polymer species and the dispersion effect was especially obvious in the comparatively high loading weight of vanadium oxide. Moreover, addition of alkaline-earth metals decreased the acidic sites of V/SBA-15, inhibiting the ring-opening reaction on which the deep oxidation occurred. The structures of all catalysts were thoroughly investigated using different characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), NH3-temperature programmed desorption (TPD), H-2 temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS), etc. A possible catalytic mechanism was proposed. (C) 2011 Elsevier B.V. All rights reserved.