Alloy catalysts of Pt-Au/C with various Pt/Au ratios were prepared for an oxygen reduction reaction (ORR). The structure, Surface species, surface compositions, and electrocatalytic activities of prepared alloy catalysts were characterized by XRD, TPR, XPS, and rotating disk electrode (RDE) techniques. respectively. it was observed that the ORR activity of the Pt75Au25/C alloy catalyst was enhanced significantly in comparison to the commercial Pt/C catalyst within the mixed kinetic-diffusion control region. The alloying with Au modified the oxophilicity of Pt-Au alloy catalysts. TPR characterization suggests that the enhancement Of Pt75Au25/C was attributed to the formation of an alloy surface, having a moderate oxophilicity and a Pt-related alloy surface species. (C) 2009 Elsevier Inc. All rights reserved.