Terbium-activated calcium tungstate (CaWO4:Tb) nanophosphors were synthesized by a hydrothermal method. The particles were proved to be spherelike, about 50 nm in diameter, which behaved in a conspicuously unique nature compared with bulk CaWO4:Tb. In virtue of the quantum size effect, the absorption curve of the nanocrystalline shifted 28 nm to the short wavelength. A higher quenching concentration and a longer decay time of the nanoscaled sample than those of the bulk were observed upon the irradiation of UV and vacuum UV light, and the phenomena could be induced by the limitation of resonant energy transfer. This observation could remedy the deficiency of nanophosphors in emission intensity and show that nanoscaled phosphor has important potential applications.