Oxidation of some aryl methyl sulfides and aryl methyl sulfoxides with hydrogen peroxide, mediated by cetylpyridinium tetrakis(diperoxomolybdo)phosphate (PCMP), was performed in chloroform/ethanol. In addition, the stoichiometric oxidation of sulfoxides to sulfones by PCMP was carried out in chloroform. Second-order rate laws, first order with respect to substrate and to PCMP, were observed in both catalytic and stoichiometric processes. Kinetic data seem to indicate that sulfides are oxidized by a bimolecular process which involves a nucleophilic attack of the substrate on the peroxidic oxygen. On the other hand, the possibility of radical incursion is suggested in the oxidation of sulfoxides. © 1991.