The photocatalytic activity of a Pt–(CdS/ZnS) system towards hydrogen generation from water and in presence of a sacrificial organic is studied. Pt–(CdS/ZnS) was prepared by two different methods. In the first one the composite was synthesized by precipitation of CdS onto the ZnS powder and subsequent loading with Pt. In the second one it was prepared by simply sintering the mixture of CdS and ZnS powders, also followed by Pt loading. The photocatalysts were characterized by X-ray powder diffraction (XRD), SEM and TEM microscopy, UV-vis absorption spectroscopy and nitrogen adsorption–desorption (BET method). The effects of preparation method, calcination temperature, catalyst loading, initial acid formic concentration, and pH on the photocatalytic activity were studied. The reusability of the photocatalyst was also tested and the presence of Cd²⁺ and Zn²⁺ in solution was evaluated to verify the existence of catalyst photocorrosion. The results show a large difference in the hydrogen generation according to the preparation method used.