The upconversion luminescent properties are investigated in Li+ and Er3+ codoped Y2O3 nanocrystals, especially the effect of the Li+ molar fraction on the crystalline structure and the luminescent intensity. Results indicate that the samples prepared by combustion method have good crystallinity even with high Li+ codoping concentration. The luminescent test results show that with the increase of the Li+ codoping concentration, the upconversion luminescent intensity of the nanocrystals in green and red range will enhance remarkably. The lattice symmetry of the nanocrystals is modified by codoping Li+, which increases the intra-4f transition probability in Er3+.