The performance of proton exchange membrane fuel cells fed with hydrogen, CO and a hydrogen - (2%) CO mixture, using oxygen in the cathode was evaluated. Six catalysts were tested for the fuels oxidation: Pt, Pt 85 Ru 15 , Pt 50 Ru 50 , Pt 90 Ir 10 , Pt 50 Ir 50 y Pt 90 Sn 10 . Cathode catalyst was pure Pt. All catalyst were supported on Vulcan XC-72R ® carbon. The catalyst compositions were verified using a scanning electron microscope (SEM) and the performance tests were carried out through current - potential curves. The results showed that the preparation method produces catalyst compositions very close to those expected. Pt-Ir catalytic mixture show the lowest performance under the conditions followed in this work. Pt 90 Sn 10 mixture presented a performance similar to Pt at low current values when the fuel cell was fed with pure hydrogen and it showed the best performance among the other catalysts when the cell was fed with H 2/(2%)CO. The Pt 90 Sn 10 electrode lost its catalytic activity when pure CO is used.