The applicability of the tin(II) polyoxometalate catalyst, [(n-C4H9)4N]5PSnMo2W9O39 · 9H2O, for sulfoxidation of diaryl, dibenzyl, aryl benzyl, dialkyl, cyclic, and heterocyclic sulfides with 30% hydrogen peroxide was examined under organic halogen-free condition. It is noteworthy that different functional groups including carbon-carbon double bonds, ketones, oximes, aldehydes, ethers, alcohols, and acetals were tolerated under this reaction condition.