A divanadium-substituted phosphotungstate [gamma-PW10O38V2(mu-OH)(2)](3-) (I) could act as an efficient homogeneous catalyst for selective oxidation of sulfides with 30% aqueous H2O2. By using I at 0.01-0.1 mol%, various kinds of sulfides including aryl, alkyl, and vinyl ones could be converted into the corresponding sulfoxides in excellent yields with one equivalent of H2O2 with respect to sulfides. The negative Hammett rho value (-0.83) for competitive oxidation of p-substituted thioanisoles and the low X-SO (X-SO = (nucleophilic oxidation)/(total oxidation)) value (<0.01) for the I-catalyzed oxidation of thianthrene 5-oxide (SSO) revealed that I produces a strong electrophilic oxidant. (C) 2012 Elsevier B. V. All rights reserved.