The electrochemical codeposition method has been used to prepare a series of Pt/MoOx/glassy carbon (GC) electrodes with different atomic ratios of Pt to Mo. The advantage of this method is the mixing of metal and support on a microscopic level (atomic or molecular scale). That is, to disperse the Pt microparticles into the molybdenum oxide on a GC substrate. The Pt/MoOx/GC electrode was prepared by scanning the electrode potential between 0.55 and -0.70 V nus. Hg/Hg2SO4 in potassium hexachloroplatinate. sodium molybdate, and 2.2 M sulfuric acid solution at a GC substrate using a scan rate of 20 mV/s. The scanning electron microscopy results show that the Pc and MoO, microparticles are uniformly dispersed on the GC electrode surfaces. in addition, the modified electrode exhibits electrocatalytic activity for the oxidation of methanol. Based on the catalytic properties, the optimal concentrations for the preparation of the composite electrode is 3.0 mM in K2PtCl6, and 300 mM of Na,MoO,. X-ray photoelectron spectroscopy (XPS) analyses indicate that the best Pt to Mo atomic ratio is in the range between 1.5 and 2.0. In addition, the XPS spectra present a broad peak in the Mo (3d) binding energy region reventing the existence of Mo6+ species as well as lower valence state Mo5+ and Mo4+. Finally, a reaction mechanism is suggested fur methanol oxidation at this composite Pt/MoOx, GC electrode. (C) 2001 The Electrochemical Society.