In this study, photocatalytic hydrogen production over metal-incorporated CdS and ZnO (M/CdS/ZnO) nanocomposites under simulated solar light illumination was investigated. M/CdS/ZnO samples were synthesized by photodepositing a metal into CdS/ZnO powders. All photocatalysts showed increased hydrogen production with an increase in the light exposure time. The M/CdS/ZnO samples exhibited better hydrogen production yields than the CdS/ZnO nanocomposites, which in turn showed higher hydrogen production yields than pure ZnO did. The hydrogen production yields of the CdS/ZnO samples increased as the CdS/ZnO weight ratio increased from 0.01 to 0.10. However, they decreased with further increases in CdS loading, although the light absorption edges of the CdS/ZnO samples were further extended to the visible region. Pt/CdS/ZnO and Pd/CdS/ZnO exhibited similar hydrogen production yields, which were higher than the Ni/CdS/ZnO yield. The hydrogen production yield of Pt (0.5%)/CdS/ZnO was higher than that of Pt (0.1%)/CdS/ZnO. Notably, the hydrogen production yield of CdS/Pt/ZnO was lower than that of Pt/CdS/ZnO. Among three different electron donors (Na2S + Na2SO3, methanol, and lactic acid solutions), the Na2S + Na2SO3 solution led to the highest hydrogen production yield. A tentative mechanism for photocatalytic hydrogen production over M/CdS/ZnO nanocomposites under solar light irradiation, using a Na2S + Na2SO3 solution as an electron donor, was proposed. In summary, M/CdS/ZnO photocatalysts can be utilized efficiently for photo catalytic hydrogen production with solar light exposure through proper control of operating parameters. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.