We have developed a novel preparation method for Pt-based nanoparticles by means of double potential step electrolysis (DPSE), in which Pt-Ni alloy deposited at the first step and Ni dissolved at the following step. A cycle of the DPSE in a nickel plating bath containing PtCl62-led to the formation of the Pt-Ni nanoparticles with size of about 5.4 +/- 1.5 nm, which gradually grew up with repeating the DPSE process, and surface Ni content of the particles by XPS was controllable by changing some parameters of the DPSE. The Pt-Ni nanoparticles deposited by the DPSE were covered with a Pt skin layer, which influence the improvement of both catalytic activity for oxygen reduction reaction (ORR) and corrosion resistance. The Pt-Ni nanoparticles by the DPSE exhibit ca. two times higher electrocatalytic activity for ORR than Pt nanoparticles, and further, of which catalytic activity was maintained high even with more than 1000 cycles of potential cycling test in H2SO4 solution, showing good corrosion resistance. (c) 2008 Elsevier Ltd. All rights reserved.