To explore the efficacy of lanthanides doping on photocatalytic performance of silver orthophosphate, Gd-doped, Dy-doped and Er-doped Ag3PO4 nanoparticles were prepared by co-precipitation method. All synthesized samples were characterized systematically. The photocatalytic activity of pure and M-doped Ag3PO4 (M = Gd, Dy and Er) was compared in degradation of an Anthraquinone dye (Ractive Blue 19). In order to comprehensive comparison, photocatalytic processes by M-doped Ag3PO4 were individually optimized by Response Surface Methodology (RSM). At the optimal conditions proposed by RSM, the photocatalytic degradation efficiency by Gd-doped, Dy-doped and Er-doped Ag3PO4 were 80.4, 92.4 and 57.8%, respectively. Due to the considerable decrease in degradation efficiency in the presence of oxalate anion and p-benzoquinone, photogenerated holes and superoxide anion radicals were detected as the main reactive species in degradation of RB19. The main role of the trivalent lanthanide cations in Ag3PO4 photocatalytic activity enhancement was also discussed. (C) 2016 Elsevier Ltd. All rights reserved.