Carbon-supported Pt-based ternary alloy electrocatalysts were prepared by incipient wetness method in order to elucidate the origin of the enhanced activity of oxygen reduction reaction in PEMFC. To measure the catalytic activity and stability of the cathode alloy catalysts (electrodes containing Pt loading of 0.3 mg/cm(2), 20 wt.% Pt/C, E-TEK), the I-V polarization Curves were obtained. All alloy catalysts showed higher performances than Pt/C. It can be concluded that as platinum formed alloys with transition metals, the electronic state of Pt and the nearest neighbor Pt-Pt distance changes, which significantly influence the electrocatalytic activity for oxygen reduction. Long-term stability test was perforined with the Pt6Co1Cr1/C alloy catalyst for 500 h. According to XPS analysis, the lower oxide component with Pt6Co1Cr1/C electrocatalyst provides a large portion of platilulln in metallic species in the electrocatalyst and it seems to be mainly responsible for its enhanced activity towards oxygen reduction. (c) 2006 Elsevier Ltd. All rights reserved.