Mn3O4- and CuO-modified zinc sulfide (ZnS) photocatalysts were successfully prepared and characterized by Xray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, surface area analysis, and diffuse-reflectance spectroscopy methods. The weight percentages of manganese (Mn) or copper (Cu) in the composite catalysts were maintained between 0.5% and 5%. Optical characterizations of the synthesized catalysts showed the shifted photoabsorption properties from the ultraviolet region to visible light. The band gaps of ZnS loaded with 0.5-5% Mn and Cu were calculated from the absorption edge positions and were in the ranges of 2.61-2.81 and 2.81-2.92 eV, respectively. The photocatalytic performances of the ZnS composites were evaluated for the visible-light-assisted photocatalytic decomposition of Orange II dye. ZnS loaded with 1.5 wt % Mn and 1 wt % Cu at a dosage of 0.5 g/L shows the highest photocatalytic activity, which represents 32.1% and 61.1% degradation of Orange II dye, respectively.