Using an inverted spontaneous deposition method, unsupported Ru and carbon-supported 40% Ru nanoparticles were decorated with platinum after surface Ru oxides were reduced in the hydrogen atmosphere at 25degreesC for 1 h. All samples that we produced in this way yielded high catalytic activity towards methanol oxidation at an electrode potential of interest to DMFC fuel cells. In the chronoamperometric experiment, the activity increased with the uptake of platinum to high Pt packing density values. The 40% C/Ru/Pt catalyst with an optimized packing density shows higher reactivity than that of an equivalent commercial, carbon-supported Pt/Ru catalyst. Reduction of Ru (and Ru/Pt) nanoparticles at higher than ambient temperature induced unacceptable level of sintering, and was avoided. (C) 2004 Elsevier B.V. All rights reserved.