The dissolution of MnS inclusions in stainless steels (SS) 303 and 304 during initiation of pitting corrosion in an aqueous solution containing 10 mM KI and 0.1 M NaCl was investigated with use of a scanning electrochemical microscope (SECM). The dissolution products of MnS were detected amperometrically at a carbon fiber SECM tip using I-/I-3(-) as the redox mediator. SECM images showed that the sulfur species are slowly generated above previously identified MnS inclusions. The SECM tip current was stable up to 100 min, depending on the potential applied to the SS 304. SECM was found to be useful in mapping local concentration distributions of sulfur and their evolution in time during dissolution.