This paper reports the preparation of ultrafine CeO 2 particles by using frozen dehydrating method and urea decomposition method. The results are compared with that of sol gel method. It is found that reaction temperature(T r), ammonia concentration(C a) and calcination temperature(T c) significantly affect the particle size and the surface area of the product for frozen dehydrating method. TEM results show that gelatinized at 0℃, CeO 2 particles with an average particle size of 7nm and a surface area...