Using the spontaneous deposition method (W Chrzanowski and A. Wieckowski, Langmuir 13, 5974 (1997)), platinum nanoparticles were decorated with ruthenium to obtain a Pt/Ru catalyst with a packing density of up to 0.65 Ru atoms per Pt surface atom. The activity of this catalyst toward methanol electrooxidation was tested at electrode potentials of interest for fuel cells. The catalyst activity maximizes at ruthenium packing density 0.4-0.5, and the catalyst is twice as active (displays higher current densities normalized to real surface area) as the commercial 50: 50 Pt/Ru alloy catalyst. Hydrogen adsorption on the decorated Pt/Ru and Pt/Ru alloy surfaces is also reported.