Preparation of Pt-Ru electrocatalyst was successfully performed on carbon paper by one-step co-electrodeposition method. Particle size and density were controlled by deposition potential and time. Coverage of the catalysts deposited on the carbon paper was significantly related to the composition of the electrolyte. Catalyst particles were characterized by field emission scanning electron microscopy (FESEM), and the crystal structure was analyzed by X-ray diffraction (XRD). Bulk and surface compositions of the electrocatalysts were obtained by inductively coupled plasma mass spectroscopy (ICPMS) and X-ray photoelectron spectroscopy (XPS), respectively. The Pt-Ru electrocatalyst with a surface molar ratio of 51.7 Pt and 48.3 Ru showed the highest catalytic activity for methanol oxidation and the strongest tolerance against carbon monoxide poisoning. (C) 2011 Elsevier B.V. All rights reserved.