Efficient noble-metal-free semiconductor composite photocatalysts are highly desirable for visible light driven water splitting. In this study, Ni2P was successfully decorated on Zn0.5Cd0.5S as a highly efficient co-catalyst via a hydrothermal method. The chemical as well as photophysical properties of the as-obtained Ni2P/Zn0.5Cd0.5S samples were characterized by X-ray diffractometry (XRD), Transmission electron microscope (TEM), UV-vis diffusion reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and time-resolved fluorescence. The Ni2P/Zn0.5Cd0.5S composite sample with 4% molar content of Ni2P showed the highest photocatalytic H-2 evolution activity with a corresponding H-2 evolution rate of 1173 mu mol h(-1), which was about 13 times higher than that of pure Zn0.5Cd0.5S sample under visible light irradiation. The photo catalytic activity of the Ni2P/Zn0.5Cd0.5S composite sample was stable even after 4 cycling photocatalytic experiments. A possible mechanism on the photocatalytic enhancement of the Ni2P/Zn0.5Cd0.5S composite sample was systematically investigated, which can provide a novel concept for the synthesis of other desirable semiconductor materials with high photocatalytic performance.