We have synthesized Se/Ru core/shell nanoparticles (NPs) as cathode electrocatalysts. By controlling the concentration of RuCl(3), we obtained Se/Ru(0.2), Se/Ru(0.7), and Se/Ru(1.1) core/shell NPs. The mass activities of as-prepared catalysts were 58.0, 32.1, and 12.5 A/g, respectively; part of these values are higher than that (2.2 A/g) of a commercial PtRu electrode and those (22.8, 28.0, and 24.5 A/g) of traditional carbon-supported Ru(x)Se(y) electrodes. The Se/Ru(1.1) electrode generated the greatest current density and was more tolerant toward poisoning in the presence of 1 M MeOH; cyclic voltammetry measurements revealed that this electrode was stable for at least 100 cycles. This is the first example demonstrating preparation of Se/Ru core/shell NPs that provided excellent catalytic activity and stability toward oxidation of MeOH. With their ease of large-scale preparation, low cost, high electroactivity, and high stability, such Se/Ru core/shell NPs have great potential for use as cathode electrocatalysts in direct MeOH fuel cells. Crown Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.