The preparation of carbon-supported Pt-Ni alloy catalysts at a 40 wt% total metal loading and with high Ni content within the alloys and their electrocatalysis for the oxygen reduction reaction has been studied. Emphasis is placed on the methanol-tolerant oxygen reduction on as-prepared alloy catalysts and their application in direct methanol fuel cells. It was found that as-prepared alloy catalysts have single-phase disordered structures and small particle sizes with a relatively narrow size distribution even at 40 wt% loading. As compared to pure Pt/C catalyst for oxygen reduction, such alloy catalysts exhibited enhanced electrocatalytic activities in pure acidic electrolyte and significantly enhanced electrocatalytic activities in methanol-containing electrolyte. The high methanol tolerance of Pt-Ni alloy catalysts during oxygen reduction could be ascribed to a lowered activity of methanol oxidation, which may originate from the composition effect and the disordered structure of the alloy catalysts. Fuel cell tests confirmed that as-prepared Pt-Ni alloy catalysts for oxygen reduction are more active than a commercial Pt/C catalyst with the same metal loading and that the maximum activity was found with a Pt/Ni atomic ratio of 2:1, which is similar to results in half-cell tests. (C) 2004 Elsevier B.V. All rights reserved.