3-Benzylsulfanyl-4,5-diphenyl-4H-1,2,4-triazole, 5-methylsulfanyl-1-phenyl- 1H-tetrazole, 2-methylsulfanyl-1H-benzimidazole, 2-benzylsulfanyl-1H- benzimidazole, and 1-butylsulfanyl-4-nitrobenzene were oxidized to the corresponding sulfoxides with chlorine dioxide using different modes of oxidant supply. The oxidation process was characterized by high chemoselectivity.