The electrochemical deposition of Pt-Ru nanoparticles on conducting polymer supports and carbon supports, as well as their electro-catalytic activities, were investigated. Pt-Ru catalysts of 3-8 nm average size were grown on supports by step-potential plating methods. The catalysts' loading contents were enhanced by increasing the plating time of the deposition method. Polyaniline and carbon blacks (CBs) were selected and compared as catalyst supports. The particle sizes and morphological structures of the Pt-Ru/support catalysts were evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical behaviors of the Pt-Ru/support catalysts for methanol oxidation were investigated according to their characteristic current-voltage curves and chronoamperometry in a methanol solution. As a result, the electrochemical activity was enhanced with increased plating time, reaching the maximum at 24 min, and then decreased. The specific current density for the polyaniline-supported catalysts was higher than that for the CBs-supported ones. The enhanced catalytic activity was related to the higher electrical conductivity of the polyaniline, the increased electrochemical surface area of catalysts, or the higher ion diffusion behaviours. (c) 2008 Elsevier B.V. All rights reserved.