Carbon nanotubes (CNT) supported platinum-ruthenium (Pt-Ru) catalysts were prepared by impregnation-reduction using an ethanolic solution of H 2PtCl6 and RuCl3. The effect of reduction temperatures on particle size, surface area and their relationship to the electrocatalytic activity for methanol oxidation were investigated. Thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS) were used for the catalyst characterization. XRD analysis showed that the PtRu/ CNT catalysts possibly consist of separate Pt and Ru phases. XPS analysis showed that the catalysts contain hydrous ruthenium oxide in addition to Pt and Ru metal and oxide species. The electrocatalytic activities of the catalysts were investigated in half-cell experiments using cyclic voltammetry, CO stripping voltammetry, chronoamperometry, and impedance spectroscopy. The results showed that the catalyst reduced at a temperature of 350°C had the largest electrochemical surface area, lowest charge transfer resistance and the highest electrocatalytic activity for methanol oxidation. The superior catalytic activity is discussed based on the presence of appropriate amount of hydrated Ru oxide. © 2009 American Chemical Society.