In this work, the plasmonic Ag/Ag3PO4/chitosan (Ag/Ag3PO4/CS) composite photocatalyst was prepared by a low-temperature strategy. Environmentally friendly CS plays triple vital roles in this composite. First, it was devoted to in situ reducing metallic silver from silver ions of Ag3PO4. Also, as the carrier of Ag/Ag3PO4 nanoparticles, CS can effectively prevent aggregation. Furthermore, benefitting from the settlement of hydrophilic CS, the prepared composite could be easily separated and recovered from the solution system. X-ray diffraction (XRD), the scanning electron microscope, energy-dispersive X-ray spectroscopy (EDS), ultraviolet-visible (UV-vis) diffused reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the properties of materials. The results of photo-decomposition testing showed that the Ag/Ag3PO4/CS composite possessed good activity for the decomposition of Rhodamine B (RhB) under visible light.