Ag3PO4 was synthesized by the precipitation method using three different types of phosphate salts (Na3PO4, Na2HPO4, and NaH2PO4) as a precipitating agent. Hydrolysis of each phosphate salt gave a specific pH that affected the purity and morphology of the prepared Ag3PO4. The Ag3PO4 prepared from Na2HPO4 showed the best photocatalytic activity induced by visible light to degrade methylene blue dye. During the photocatalytic process, Ag3PO4 decomposed and produced metallic Ag, and this evidence was confirmed by the X-ray diffraction technique and X-ray photoelectron spectroscopy. The photocatalytic efficiency decreased with the number of recycles used. This Ag3PO4 photocatalyst also degraded another cationic dye, rhodamine B, but did not degrade reactive orange, an anionic dye. The degraded products produced by the photocatalysis had lower toxicities than the untreated dyes using Chlorella vulgaris as a bioindicator.