ZnS@g-C3N4 composite photocatalysts were synthesized by an in situ thermal polycondensation process under an inert atmosphere. The physicochemical properties of the ZnS@g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and photoluminescence (PL) spectroscopy. The characterization results displayed fine ZnS nanoparticles adhered to the surface of g-C3N4 nanosheets, and the presence of ZnS nanoparticles caused the split and exfoliation of g-C3N4 nanosheets. The ZnS@g-C3N4 composite photocatalysts exhibited the apparent visible-light absorption and the weakened recombination of photogenerated electron/hole pairs. The evaluation on photocatalytic degradation of rhodamine B (RhB) indicated the ZnS@g-C3N4 composite photocatalysts possessed large adsorption capacity and superior visible-light induced activity. Based on the trapping experiments of active species, the photocatalysis mechanism of the ZnS@g-C3N4 composite photocatalysts was also discussed. [GRAPHICS] .