The anodic oxidation of sulfide species on a platinum electrode in alkaline solutions has been studied using a wide variety of techniques. Sulfide oxidation results in the formation of a surface layer containing platinum(IV) sulfide and sulfur, that passivates the electrode. Further oxidation is possible only after this layer is removed either by oxidation or reduction. Oxide formation is inhibited in sulfide solutions because of the competing adsorption of S2− and HO−. Similarly, sulfide oxidation to sulfur is practically eliminated on oxide covered surfaces. At high enough potentials, oxidation to sulfate is again possible. The oxide film can be chemically removed at high sulfide concentrations, resulting in further sulfur deposition. The electrocatalytical activity of sulfur deposits towards the oxidation of several compounds (e.g., methanol, CO, formic acid) is probably related to the inhibition of oxide formation. From the potential dependence of the electrode impedance some solid state properties (dielectric constant, resistivity) and the thickness of the surface film have been estimated.