In this research, a novel KIT‐5/Bi2S3‐Fe3O4 nanocomposite was prepared. The structure and morphology properties of the nanocomposite were well characterized by XRD, FESEM‐EDS‐mapping, TEM, and N2 adsorption–desorption. Benefiting from the visible light, the as‐prepared KIT‐5/Bi2S3‐Fe3O4 nanocomposite exhibit significantly improved photocatalytic performance for the degradation of parathion. The optimum photocatalytic efficiency of KIT‐5/Bi2S3‐Fe3O4 nanocomposite was investigated with the central composite design using Design Expert software. The four critical variables affecting parathion degradation such as the concentration of parathion, pH, irradiation time, and amount of KIT‐5/Bi2S3‐Fe3O4 nanocatalyst. A polynomial function corresponding to degradation percent was obtained for the experimental data. The results showed that this catalyst has a good performance for the degradation of parathion.