The PtRu alloying degree was controlled by mixing various amounts of water in the solvent while the nominal Pt/Ru ratio was remained at the value of one, and the relationship between the alloying degree and electrochemical activities was examined in this study. X-ray diffraction analysis showed that the fraction of the alloyed Ru ranged from approximately 18% for 100% water solvent to 86% for 0% water solvent. In X-ray photoelectron spectroscopy (XPS), Pt and Ru metallic components increased with the PtRu alloying degree. Electrochemical activities for CO oxidation and methanol oxidation were enhanced as the PtRu alloying degree became higher. Electrochemical stability was also investigated via potential cycling in a methanol-contained electrolyte solution. After the potential cycling process, the catalysts were analyzed by transmission electron microscopy, XPS, XPS element mapping. Possible reasons for the difference in the electrochemical stability of the catalysts were discussed. (C) 2010 Elsevier BM. All rights reserved.