This paper introduces HER activity of a string of Ni-P nanoparticles. The hydrogen evolution reaction (HER) activity of different Ni-P nanoparticles hinges on elemental ratios of nickel to phosphorus and nickel phosphide phases through annealing processes, which lead to utter diverse HER performances in H2SO4 and NaOH. The sample annealed under 350 A degrees C by 4 h, mainly comprised by Ni3P and Ni12P5, shows overpotential of 333 mV to achieve 100 mA center dot cm(-2) (eta(100) = 333 mV) current density in acidic condition, whereas in alkaline condition, the non-heat-treated sample, mainly formed by Ni12P5 and Ni2P, shows the best HER performance. Ni-P nanoparticles have also displayed distinguished durability in both H2SO4 and NaOH. The superior HER activity and durability are supported by a series of characterizations and stem from Ni-P nanoparticles' nature, including their morphology, good ensemble effect between nickel and phosphorus, and anti-corrosive quality.