For the development of a novel anode catalyst for use in a DMFC, Pt oxide blacks were partially reduced by electrochemical treatment, and the electrocatalytic activities of the methanol oxidation were investigated by the rotating disk electrode method. Specific surface area measurement of the active sites by CO stripping voltammetry, analysis of the chemical shift by XPS and determination of the O/Pt atomic ratio by EPMA were also carried out on the reduced Pt oxide blacks. Compared to the Pt oxide black without reduction, the methanol oxidation activity of the partially reduced Pt oxide black was significantly improved by applying the cathodic charge of -0.6 C or more. The Pt oxide black reduced by -1.2 C had particularly good properties, namely, the anode catalyst showed both the highest current density and the minimum activation energy of the methanol oxidation. The methanol oxidation activity of the Pt oxide black, which was effectually enhanced by the electrochemical reduction, exceeded that of the anode catalyst now in use or PtRu black. Furthermore, the XPS and EPMA analyses suggested that the residual oxygen in the partially reduced Pt oxide black played an important role in the methanol oxidation.