A temperature dependence for emission of Eu3+ in cubic nanocrystalline Y2O3:Eu3+ was studied in contrast with the polycrystalline powders. The emission intensity of Eu3+ decreased solely with elevated temperature under the excitation of a 580 nm light, while it had a maximum at a certain temperature under a 488 nm light. The experimental data were well fitted based on a theory considering both the thermal activated distribution of electrons among F-7(J) and the thermal quenching effect. The results indicated that the thermal quenching rate in nanocrystals (NCs) was faster than that in the polycrystals. The nonradiative decay rate, w(NR), the radiative transition rate, w(0R), and the luminescent quantum efficiency (QE) were obtained according to the temperature dependence of fluorescence lifetime. It can be concluded that w(NR) and w(0R) both increase in NCs, and that QE decreases. (C) 2003 American Institute of Physics.