Bi3+ doped Cd0.5Zn0.5S photocatalysts were prepared by a simple hydrothermal method, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), energy dispersive X-ray spectroscopy (EDX), BET and UV-Vis absorption spectroscope techniques. When Bi3+ doping content is lower, the doping ions lie at the surface lattice sites, whereas when the doping content is higher, the ions also enter the bulk lattice sites. Their photoactivities were evaluated by hydrogen evolution from aqueous solution containing Na2S and Na2SO3 as a hole scavenger under visible light (lambda >= 420 nm) irradiation. Bi3+ doping enhances markedly photocatalytic activity. When Bi3+ doping content is 0.10 mole %, the photocatalyst exhibits the highest activity, and the average apparent quantum yield amounts to 9.71% during 30 h irradiation. The possible mechanism was discussed. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.