Nanocrystalline nickel phosphide (Ni₁₂P₅) was successfully synthesized by a simple hydrothermal method via using NiCl₂ and red phosphorus as raw materials. The crystal structure, morphology and surface chemical compositions of the as-prepared sample were characterized by X-ray diffraction, scanning electron microscope and X-ray photoelectron spectroscopy techniques, respectively. Its catalytic activity for the hydrogen evolution from water was investigated under visible light irradiation (λ ≥ 420 nm) with fluorescein sodium as the photosensitizer and triethanolamine as the sacrificial electron donor, respectively. The results indicated that the Ni₁₂P₅ sample showed high catalytic activity (10 760 μmol h⁻¹ g⁻¹, TOF = 9.3 h⁻¹) and good stability (15 h) in the present system. The electrochemical results revealed that Ni₁₂P₅ had a high cathodic current and small charge transfer resistance, which further suggested Ni₁₂P₅ indeed could efficiently catalyze the evolution of hydrogen.