In this study, a novel ZnS/MoS2/Fe3O4 magnetic nanocomposite was synthesized via hydrothermal and co-precipitation methods. The ZnS/MoS2/Fe3O4 nanocomposite was synthesized by loading ZnS with MoS2 semiconductor and Fe3O4. Different methods and analyses were used to identify and characterize the binary ZnS/MoS2 and ternary ZnS/MoS2/Fe3O4 nanocomposites. The X-ray diffraction patterns confirmed the formation of cubic structures of ZnS and Fe3O4 and hexagonal structure of MoS2. The electron microscopy images affirmed the well formation of nano structure of the composite. The photoluminescence intensity of the ZnS/MoS2/Fe3O4 nanocomposite decreased due to the reduced electron-hole recombination in the ZnS/MoS2/Fe3O4 sample compared to the ZnS/MoS2 one. The photocatalytic activity of ZnS/MoS2/Fe3O4 magnetic nanocomposite on the dye degradation of Naphthol Green was investigated under UV-Vis irradiation. The effective factors of the photocatalytic degradation including pH, photocatalyst type and dosage as well as radiation type were optimized. The ternary nanocomposite showed greater photocatalytic efficiency compared to the binary one, being 84% and 97% in visible and ultraviolet light radiations, respectively; this is due to the reduced electron-holes recombination and band gap energy. It also displayed highly stable recycling performances since it can be separated rapidly with a simple magnet. The involved ternary heterostructural nanocomposite is an effective and promising photocatalyst for degradation of Naphthol Green in aqueous solution.