Nanocomposites between beta-WC and Pd nanoparticles supported on carbon are synthesized and their electrocatalytic properties for the hydrogen oxidation reaction have been investigated. The Pd nanoparticles are obtained by a chemical reduction reaction of PdCl2 and the beta-WC nanoparticles by a sonochemical decomposition of W(CO)(6) on Pd-loaded carbon followed by heat-treatment. Depending on the relative amounts of W to Pd, the Pd nanoparticles can be reacted with W to form Pd-W alloy nanoparticles. The Pd-W alloy, whose composition is estimated to have W less than 18 at.% based on its lattice parameter, lost most of the catalytic activity of Pd. On the other hand, the nanocomposite between P-WC and pure Pd shows an enhanced activity compared with that of Pd nanoparticles alone. This enhancement can be explained with the H+-spill-over to beta-WC. (C) 2009 Elsevier Ltd. All rights reserved.