Powder of nanosized particles of Ru-based (Ru x , Ru x Se y and Ru x Fe y Se z ) clusters were prepared as catalysts for oxygen reduction in 0.5M H2SO4 and for fuel cells prepared by pyrolysis in organic solvent. These electrocatalysts show a high uniformity of agglomerated nanometric particles. The reaction kinetics were studied using rotating disk electrodes and an enhanced catalytic activity for the powders containing selenium and iron was observed. The Ru-based electrocatalysts were used as the cathode in a single prototype PEM fuel cell, which was prepared by spray deposition of the catalyst on the surface of Nafion® 117 membranes. The electrochemical performance of each single fuel cell was compared to that of a platinum/platinum conventional membrane electrode assembly (MEA), using hydrogen and oxygen feed streams. A maximum power density of 140mWcm−2, at 80°C with 460mAcm−2 was obtained for the Ru x Fe y Se z catalysts; approximately 55% lower power density than that obtained with platinum.