Pd@Pt nanoparticles with a three-dimensional (3D) nanospherical shape have been prepared using a two-step approach in which the Pd nanospheres are synthesized controllably by a solvothermal method, and then a Pt monolayer is deposited on the Pd nanospheres using an underpotential deposition process. We systematically investigate (i) the influences of temperature and additive on the morphology of the Pd nanoparticles and (ii) the electrochemical activity of Pd@Pt for the oxygen reduction reaction (ORR). The Pd@Pt nanoparticles exhibit enhanced activity towards the ORB.. The mass activity of Pt in the Pd@Pt nanospheres (1.03 A mgPt(-1)) is 3.3 times higher than that of commercial Pt/C (0.24 A mgPt(-1)). The catalyst enhanced activity may result from the 3D structure of the Pd nanospheres and the monolayer dispersion of Pt on the surface of the nanoparticles. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.