Silver orthophosphate semiconductor was synthesized by the ion-exchange method using AgNO3 and Na2HPO4.12H2O as starting materials. The molar ratio of AgNO3 and Na2HPO4.12H2O was designed as 3:1. The product was characterized using XRD, SEM and DRS. The photocatalytic activity was determined using phenol oxidation under LED lamps with various wavelengths of visible lights such as 627nm (red), 530 nm (green) and 445 nm (blue). The body-centered cubic structure of silver orthophosphate with 1-10 μm in diameter was successfully synthesized. The band gap energy of the material could be found as 2.42 eV. The excellent photocatalytic activities of silver orthophosphate for phenol oxidation could be obtained under blue light (λ= 445nm) irradiation. The photocatalytic ability of Ag3PO4 under blue light irradiation was not lost even after heat treatment at 700°C.