Nanocrystalline La2O3 was prepared by sol-gel process using common La2O3, HNO3 and PEG. The decomposition process of the precursor powder and the calcened nanocrystalline La2O3 formed at the end were charactered with various techniques: TG-DTA, XRD and TEM and the effects of some factors such as pH value of the solution, stirring rate and the amount of the PEG in the solution on the particle size and morphology are investigated. The result shows that the nanocrystalline La2O3 can be obtained with particle diameter of 30 nm~50 nm under appropriate conditions.