Rare-earth ion (Ce3+, Tb3+) doped LaPO4 nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and lifetimes. The results of XRD indicate that the as-prepared nanoparticles are well-crystallized at 160 degrees C and assigned to the monoclinic monazite structure of the LaPO4 phase. The obtained LaPO4:Ce3+, Tb3+ nanoparticles are spherical with narrow size distribution and average size of 20 nm. The doped rare-earth ions show their characteristic emission in LaPO4 nanoparticles, i.e., Ce3+ 5d-4f and Tb3+ 5D4-7FJ (J = 6-3) transitions, respectively. The optimum doping concentration for Tb3+ in La(0.8-x)Ce0.2TbxPO4 nanoparticles is determined to be 15 mol% (x = 0.15). The luminescence decay curves of Ce3+ in LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ nanoparticles present a single-exponential behavior, and the lifetimes (tau) of Ce3+ decrease with increasing Tb3+ concentrations (at the constant Ce3+ concentration) in LaPO4:Ce3+, Tb3+ nanoparticles due to the energy transfer from Ce3+ to Tb3+. The energy-transfer efficiency from Ce3+ to Tb3+ was calculated, which depends on the doping concentrations of Tb3+ if the concentration of Ce3+ is fixed.