Carbon-supported Pt-Co electrocatalysts in the Pt:Co atomic ratio 85:15, mainly for application in polymer electrolyte fuel cells, have been prepared by different methods. The materials were tested in single cells with respect to the oxygen reduction reaction and their performances were compared. Of the several methods considered, the preparation of the electrocatalyst via the deposition and reduction of a Co precursor on previously formed carbon-supported platinum gave the best results. By increasing the Co content, a decrease of metal particle size and an improvement in the activity for the ORR of these catalysts was observed. For the electrocatalysts with a Pt:Co atomic ratio of 75:25, a good stability upon cycling was also found.