Novel magnetically separable nanocomposite photocatalyst Ag3PO4/ZnO/Fe3O4, prepared by the coprecipitation and microwave assisted hydrothermal synthesis, was first investigated as the photocatalyst for congo red degradation under visible light. The nano photocatalysts were systematically characterized with by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), vibrational sample magnetometer (VSM) measurements and UV-vis diffuse reflectance/absorbance spectroscopy (DRS). The nanocomposite Ag3PO4/ZnO/Fe3O4 showed enhanced photocatalytic activity compared with ZnO, ZnO/Fe3O4, Ag3PO4/ZnO under the same conditions. The reasons for the highly increased activity of Ag3PO4/ZnO/Fe3O4 are that it allows more visible light absorption and efficient delaying the recombination of charge carriers. Also, the degradation efficiency for congo red is about 97.0% for the Ag3PO4/ZnO/Fe3O4 nanocomposite in the 90 min. At the end of the successful degradation process, the obtained magnetic photocatalyst was effectively separated from the suspension by applying external magnetic field.