Nanometer Perovskite-type complex oxide LaFeO3 was prepared by sol-gel method using citrate ion as ligand. The influence of the amounts of citric acid, the types and amounts of dispersant, the calcining temperature and time on particle size have been studied. The formation process of LaFeO3 was also investigated by XRD, TEM, FT-IR and Raman spectroscopy. The most uniform particles with average size of 21.8nm after calcination at 650°C for 4h were found in the case of La:Fe:citric acid molar ratio=1:1:4. After adding suitable amounts of dispersant such as ethanol, propanol, isopropanol or acetic acid, the homogeneity was improved, and even smaller average size of the particles was obtained. After calcined at 800°C for 4h or 650°C for 9h, the particles were sintered partially to reach an average particle size of 26.4 nm and 34nm respectively. The XRD, TEM, IR and Raman results reveal that the decomposition of semidecomposed precursor and crystallization of nanometer LaFeO3 are completed in the temperature range of 450°C–550°C.