Efficient H2O2-based oxidation systems with three kinds of polyoxometalates, [gamma-SiW10O34(H2O)(2)](4-) (1), [gamma-1,2-H2SiV2W10O40](4-) (2), and [W2O3(O-2)(4)(H2O)(2)](2-) (3) are reported. The compound 1 can catalyze epoxidation of various olefins including non-activated terminal olefins such as propylene and 1-octene with >= 99% selectivity to epoxide and >= 99% efficiency of H2O2 utilization. It is notable that 2 shows unique stereospecificity, regioselectivity, and diastereoselectivity for the epoxidation of cis/trans olefins, non-conjugated dienes, and 3-substituted cyclohexenes, respectively. The epoxidation of various allylic alcohols with only 1 equiv. H2O2 in water can be efficiently catalyzed by 3 to give the corresponding epoxy alcohols in high yields. Further, the catalyst 3 can be recycled with the maintenance of the catalytic performance. (C) 2006 Elsevier B.V All rights reserved.