The development of high efficient electrocatalysts in water electrolysis is of great importance for sustainable hydrogen production. Herein, monodispersed bimetallic PdxCu100-x nanoparticles with average size about 4.7 nm are prepared by a one-pot method in oleylamine medium. Electrochemical measurements toward hydrogen evolution reaction (HER) indicate that both the activity and stability of carbon black loaded PdxCu(100-x) nanoparticles (PdxCu100-x/C) are highly dependent on the Pd/Cu atomic ratios. Among these electrocatalysts, Pd71Cu29/C exhibits the best electrocatalytic activity in terms of onset potential (75 mV vs. RHE), exchange current density (0.38 mA cm(-2)) and Tafel slope (48 mV dec(-1)) in 0.1 M H2SO4 among these nanoparticles. It is found that the activity toward HER of Pd71Cu29/C is better than that of commercial Pd/C and most of Pd-based electrocatalysts ever reported before. Moreover, Pd71Cu29/C shows superior catalytic stability to the commercial Pt/C. The superior HER activities and high durability (after 1000 CV cycles) of Pd71Cu29/C should be attributed to small size, the synergy effect between Cu and Pd. This work provides a facile strategy to develop the effective and stable Pt-free electrocatalyst for hydrogen generation. (C) 2017 Elsevier Ltd. All rights reserved.