Ytterbium oxide (Yb 2 O 3 ) nanocrystals with different Eu 3+ (1%, 2%, 5%, and 10%) doped concentrations were synthesized by a facile hydrothermal method, subsequently by calcination at 700°C. The crystal phase, size, and morphology of prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the as-prepared Yb 2 O 3 nanocrystals with sheet- and tube-like shape have cubic phase structure. The Eu 3+ doped Yb 2 O 3 nanocrystals were revealed to have good down conversion (DC) property and intensity of the DC luminescence can be modified by Eu 3+ contents. In our experiment the 1% Eu 3+ doped Yb 2 O 3 nanocrystals showed the strongest DC luminescence among the obtained Yb 2 O 3 nanocrystals.