Kinetics and product distribution of the reaction of dimethylsulfoxide (DMSO) and methanesulfinate (MSI ^-) with OH radicals and H ₂O ₂ in the aqueous phase are reported in this work. DMSO is found to be very stable in pure water or in solutions containing H ₂O ₂. On the other hand, it reacts very rapidly (k=4.5×10 ⁹M ^-1s ^-1) with OH radicals. MSI ^- has been identified as the main intermediate product, while methanesulfonate (MS ^-) and sulfate were the final products due to the very fast reaction of MSI ^- with OH radicals (k=1.2×10 ¹⁰M ^-1s ^-1). MS ^- has been identified as the major end product (yield higher than 95%) of both DMSO and MSI ^- reactions by OH radicals in aqueous solutions. The potential implications of these reactions for the biogenic sulfur cycle in the atmosphere are presented and discussed.