Gd2O3:Yb/Er(Tm)@microcrystals with core-shell structure were prepared by homogeneous precipitation method and then annealed at high temperature. The nanoparticles characterized by transmission electron microscopy (TEM) can be seen that the Gd2O3 with the size of about 200 nm has good dispersion, and it is proved a layer of 27 nm successfully coating the Gd2O3. The XRD patterns match well with the Gd2O3 standard card, which suggests that Gd2O3 coated by homogeneous shell do not change the structure. Moreover, the Gd2O3 shell makes the light-emitting ions isolated from the outside, while promoting the crystallization of the crystals. The high concentration of the Yb3+ as the sensitizer can absorb most of the pump light at 980nm. Therefore, the main energy transfer for the excited states of Er3+ (Tm3+) comes from Yb3+ ions. The green emissions in the region of 528 nm and 548 nm are attributed to the transitions: 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively; the red emission in 672nm corresponds to 4F9/2 → 4I15/2 transition. Moreover, the energy from the Yb3+ promotes the 3H6 level of the Tm3+ to 1G4. The blue emission at 475nm comes from the 1G4 → 3H6 and 1D2 → 3F4 transition of Tm3+ ions, whereas the emission in 653nm and 795nm are signed to 1G4→ 3F4 and 1G4→ 3H5 transitions. Meanwhile, the possible mechanims for the emissions are discussed about excited absorption and energy-transfer processes.