Ag/Ag3PO4-doped BiPO4 (Ag/Ag3PO4/BiPO4) heterostructures were synthesized by the hydrothermal method combined with the sonochemical process. Transmission electron microscopy and UV-Vis diffuse reflectance spectroscopy were used to characterize the heterostructures. The morphologies and optical properties of the heterostructures were determined to be drastically different from those of BiPO4. Ag/Ag3PO4/BiPO4 was used in the photocatalytic degradation of a dyestuff (methylene blue) and the disinfection of pathogens (Escherichia coli) under visible light (Λ > 420 nm) irradiation, and it displayed considerably higher photocatalytic activity (>99% degradation and >99% disinfection within 20 min) than did pure BiPO4. This enhanced photocatalytic activity of the Ag/Ag3PC>4/BiPO4 heterostructure can be attributed to the high separation efficiency and low recombination rate of photogenerated electron-hole pairs, as well as the Ag+ ions release under visible light irradiation.