Nanocrystalline Yb 2O 3 of various particle sizes was prepared using sol gel method. XRD analysis shows that the prepared nanocrystalline Yb 2O 3 is cubic in structure with space group Ia3. TEM photographs indicate that Yb 2O 3 nanoparticles are basically spherical in shape. Calculation of crystallite size indicates that the average crystallite size of Yb 2O 3 increases with increasing calcination temperature, but the average crystal lattice distortion rate decreases with increasing calcination temperature and crystallite size. This reault shows that the smaller the crystallite size, the bigger the crystal lattice distortion, and the worse crystal growth. Solubility test of Yb 2O 3 in nitric acid shows that the surface activity of Yb 2O 3 increases with decreasing crystallite size. Fourier Transform Infrared Spectrometer (FTIR) spectra reveal that nanocrystalline Yb 2O 3 has higher surface activity than that of ordinary Yb 2O 3. Absorbance intensity of Yb O bond of nanocrystalline Yb 2O 3 is weaker than that of ordinary Yb 2O 3, and the absorbance of Yb O bond of nanocrystalline Yb 2O 3 is small blue shifted.