To resolve the problems of the lack of cost- effective replacements of Pt catalysts and CO poisoning of Pt electrocatalysts for polymer electrolyte membrane fuel cells, we developed a state-of-the-art electrocatalyst in which a Pt layer with a thickness of a few molecular layers is spread over SnO2 nanoparticles on multiwalled carbon nanotubes. The electrocatalysts showed not only excellent activity in H adsorption/ desorption, but also a lower potential for initiating the electro-oxidation of CO in comparison with that of conventional Pt/ carbon catalysts. (c) 2005 The Electrochemical Society.