When YVO4:Eu3+ nanophosphors synthesized by a low-temperature wet chemical process in the presence of citrate ions are continuously excited by UV light, the photoluminescence (PL) intensity gradually decreases. This photobleaching is accompanied with the reduction of V5+ to V4+, as confirmed by electron paramagnetic resonance spectroscopy. Hydrothermal treatment of YVO4:Eu3+ nanophosphors in the presence of PO4 3- ions produces Y(V,P)O4:Eu3+ through the partial replacement between VO4 3- and PO4 3-, and hence results in the increase in the PL intensity and the suppression of photobleaching.