CeO 2 nanoparticles hydrosol was synthesized by colloidal chemical method. The optimum experiment conditions for the preparation of CeO 2 nanoparticles hydrosol were discussed. The effects of pH values, the reactant concentration and temperature on peptization process were studied. TEM photos showed that the CeO 2 nanoparticles were spherical in shape and the size was about 3nm. Particle size distribution was in narrow range, and no agglomerates were observed. ED images indicated that the CeO 2 nanoparticles were polycrystalline structure, and some of CeO 2 were monocrystal particles.