Ternary Pt-based nanoparticles (nominal composition Pt80Ru10Sn10 ) were synthesized via the microemulsion route and deposited onto boron-doped diamond (BDD) electrode. The particle size measured by transmission electron microscopy was in the 2–5nm diam range. X-ray photoelectron spectroscopy revealed a slightly different surface composition from that of the bulk and showed no chemical shift of the Pt4f7∕2 line in ternary Pt∕Ru∕Sn nanoparticles. For both methanol and ethanol electro-oxidation, the ternary catalyst exhibited lower onset potentials than either pure Pt or the corresponding bimetallic (Pt∕Ru and Pt∕Sn ) catalysts. The ternary Pt∕Ru∕Sn catalyst was more efficient for methanol oxidation than for complete oxidation of ethanol, because ethanol electro-oxidation was stopped at acetaldehyde and/or acetic acid formation, the ternary catalyst being unable to activate the C-C bond scission.