Nanosized Pt and PtRu colloids were prepared by a microwave-assisted polyol process and transferred to a toluene solution of decanthiol. Vulcan XC-72 was then added to the toluene solution to adsorb the thiolated Pt and PtRu colloids. TEM examinations showed nearly spherical particles and narrow size distributions for both supported and unsupported metals. The carbon-supported Pt and PtRu nanoparticies were activated by thermal treatment to remove the thiol stabilizing shell. All Pt and PtRu catalysts (except Pt23Ru77) showed the X-ray diffraction pattern of a face-centered cubic (fee) crystal structure, whereas the Pt23Ru77 alloy was more typical of the hexagonal close-packed (hcp) structure. The electro-oxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results showed that the alloy catalyst was catalytically more active than pure platinum. The heat-treated catalyst was also expectedly more active than the non-heat-treated ones, because of the successful removal of the organic shell, which might interfere with reactant adsorption in the methanol oxidation reaction. Pt52Ru48/C had the best electrocatalytic performance among all carbon-supported Pt and PtRu catalysts.