We synthesized three kinds of Pt-Ru/C catalysts (denoted as a, b, and C) through conventional polyol process by heating the reaction Solutions to different temperatures (120, 160 and 180 degrees C, respectively) and the fourth kind of catalyst (denoted as d) through 3 modified polyol process at 180 degrees C. By using scanning transmission electron microscopy combined with energy dispersive X-ray line analysis, we found that a higher reaction temperature resulted in more uniform particle-compositions of the Pt-Ru catalysts, which Could be ascribed to the influence of temperature oil the reduction rates of metal ions. The Pt-Ru/C-a catalyst showed a bimodal particle-composition distribution, while the Pt-Ru/C-d catalyst showed the narrowest unimodal distribution due to the highest temperature throughout the reaction. X-ray diffraction showed that all the Pt-Ru/C catalysts exhibited low alloying degrees of Ru with Pt. Front high resolution transmission electron microscopy, we confirmed that the un-alloyed Ru was present in an amorphous form (likely RuOx), and moreover, its distribution varied greatly in different catalysts. In the Pt-Ru/C-d catalyst, the amorphous RuOx intimately contacted with the Pt/Pt-rich alloy, forming nano-composite particles. The Most uniform compositions of Pt-Ru particles in the Pt-Ru/C-d catalyst resulted in the highest electrocatalytic activity oil methanol oxidation. (C) 2009 Elsevier B.V. All rights reserved.