Nanosize carbon-supported Pt1-xCox (x = 0.2, 0.3, and 0.45) electrocatalysts were prepared by a chemical reduction method using sodium borohydride (NaBH4) as the reduction agent. Transmission electron microscopy examination showed uniform dispersion of Pt1-xCox alloy catalysts on carbon matrix, with the particle size less than 10 nm. The electrochemical characteristics of Pt1-xCox alloy catalysts were studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometric testing. The as-prepared Pt1-xCox alloy nanoparticles could be promising cathode catalysts for oxygen reduction in proton exchange membrane fuel cells with the feature of much reduced cost, but significantly increased catalytic activity. (C) 2010 Elsevier B.V. All rights reserved.