The catalytic activity of carbon supported Pd-Co-Mo for the oxygen reduction reaction (ORR) in a single cell proton exchange membrane fuel cell (PEMFC) has been investigated at 60 degrees C and compared with data front commercial Pt catalyst and our previously reported Pd-Co-Au and Pd-Ti catalysts. The Pd-Co-Mo catalyst with a Pd:Co:Mo atomic ratio of 70:20:10 exhibits slightly higher catalytic activity like the Pd-Co-AU catalyst than the commercial Pt catalyst, but with excellent chemical stability unlike the Pd-Co-Au catalyst. The Pd-Co-Mo catalyst also exhibits better tolerance to methanol poisoning than Pt. Investigation of the catalytic activity of the Pd-Co-Mo system with varying composition and heat treatment temperature reveals that a Pd:Co:Mo atomic ratio of 70:20: 10 with a heat treatment temperature of 500 degrees C exhibits the highest catalytic activity. Although the degree ofalloying increases with increasing temperature from 500 to 900 degrees C as indicated by the X-ray diffraction data, the catalytic activity decreases due to an increase in particle size and a decrease ill Surface area.