Pt3Co/C electrocatalysts prepared by wet synthesis method from water-ethylene glycol solutions of Pt and Co precursors were investigated by X-ray diffraction in conjunction with electrochemical measurements. It was shown that varying the binary solvent composition is an effective means of control over the average nanoparticle size and the rain size distribution. It was found that unit cell parameter of the Pt3Co/C electrocatalysts decreases nonlinearly with decreasing particle size. The activity of the prepared Pt3Co/C catalysts for the oxygen reduction reaction (ORR) in H2SO4 solution enhances with decrease in the particle size, the unit cell parameter, and the dispersion of the grain size distribution All. samples studied show higher catalytic activities in comparison with the commercial Pt/C materials. (C) 2008 Elsevier B.V. All rights reserved.