Carbon supported Pt-Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid, and their electrocatalytic activity for methanol oxidation was compared with commercial Pt/C and Pt75Sn25/C electrocatalysts. By X-ray diffraction analysis it was found that the Pt lattice parameter increases with the addition of Sn, indicative of alloy formation. It was confirmed that Sn exhibits cocatalytic activity for CO oxidation. The onset potential for the methanol oxidation reaction of the Pt-Sn electrode was approximately 0.1 V smaller than that on Pt both at room temperature and at 90 degrees C. The best performance in a direct methanol fuel cell was obtained using the Pt75Sn25/C alloy catalyst prepared by the formic acid method as the result of an optimal balance of Sn content, degree of alloying and metal particle size. (C) 2005 Elsevier Ltd. All rights reserved.