This communication reports the synthesis of mesoporous Pd-Co dendrites with both a unique hierarchical porosity and a large surface area by the combination of electrodeposition and dealloying. The resultant mesoporous dendrites consist of microparticles with a diameter of a few hundred nanometers, and the particles have mesopores with around 10 nm width. The mesoporous dendrites are found to be Pd8Co2, to be composed of pure Pd crystalline phases and amorphous Pd-Co phases, and to be covered with Pd-skin layers. This catalyst exhibits a high activity in the oxygen reduction reaction. Thus, this novel catalyst is attractive as a catalyst for on-chip fuel cells. which require catalysts to be deposited precisely onto tiny current collectors. (C) 2009 Published by Elsevier B.V.