Department of Post-Graduate Studies and Research in Chemistry, Mangalore University, Mangalagangothri-574 199, India E-mail : gowdabt@yahoo.com Fax : 91-824-742367/742424 Manuscript received 10 October 2000, accepted 22 March 2001 Kinetics of oxidation of dimethylsulfoxide (DMSO) by N-halosulfonamides (chloramine-B, chloramine-T, dichloramine-B and dichloramine-T) have been studied in 1 : 1 (v/v) water-methanol and water-acetic acid media in the presence of perchloric acid. The rates show first order kinetics in [oxidant], fractional to first order in [DMSO] and zero order in [H+]. Variation in ionic strength of the reaction medium or addition of the reduced products of oxidants has no significant effect on the rates of oxidations. But the rates decrease with decrease in dielectric constant of the reaction medium by increasing the methanol or acetic acid composition of the solvent. Two-pahway as well as Michaelis-Menten type mechanisms have been considered to explain the observed results. The activation parameters have also been computed.