In order to survey new CO-tolerant anode for the PEFC application, the addition of TaOx and NbOx to the Pt catalyst was examined in the electrochemical oxidation of CO in a sulfuric acid solution. Voltammetric peak potentials for the oxidation of CO pre-adsorbed on the Pt surface shifted to lower potentials by these additives, indicating an enhancement of electro-catalysis of Pt for the CO oxidation. Both oxides of Ta or Nb also bring about an inhibition of the CO adsorption rate onto the Pt surface. Concerted effect of these oxides with Ru is discussed for the CO oxidation over the PtRu-TaOx, and the PtRu-NbOx anodes. (C) 2003 Elsevier Science B.V. All rights reserved.