We proposed a facile route to one-step synthesis of well-dispersed PtCo alloy nanoparticles with dendritic morphology. Platinum acetylacetonate [Pt(acac)(2)] and cobalt acetylacetone [Co(acac)(2)] were chosen as the precursors to prepare PtCo alloy nanoparticles under a relatively mild condition with anhydrous ethylenediamine and poly(vinyl pyrrolidone) (PVP) as solvent and surfactant, respectively, in the presence of NaBH4. Structural characterizations with transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) revealed that PtCo nanoparticles possess an interesting dendritic morphology with excellent structural continuity and integrity. As an alternative cathodic electrocatalyst, PtCo nanodendrites (NDs) showed very high activity for oxygen reduction reaction (ORR) with half-wave potential at similar to 0.877 V (versus RHE), which is nearly 50 mV more positive as compared with that of the commercial Pt/C catalyst (0.828 V). The Pt mass activity and specific activity were 0.11 A/mg(pt) and 0.68 mA/cm(2), respectively (similar to 1.5 and similar to 4.5 times higher than the corresponding values for the commercial Pt catalysts), at 0.9 V. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.