Nanograde cerium oxide is formed successfully by a normal-pressure aging process via cerium sulfate. The nanograde cerium oxide is formed by the precursor of cerium Sulfate decomposition during aging in urea solution. There are two pH stages in the aging process: one is in pH = 5-6 and the other is in pH = 7-8. The first pH stage is the particle decomposed stage in which the particles were decomposed gradually. In the last stage, the final product is uniform aggregated particles which are formed by complete decomposition. The crystalline size of cerium oxide formed by this method is about 6-7 nm. The decomposed rate of precursor is increased by increasing urea concentration or increasing the aging time, respectively. (c) 2005 Elsevier B.V. All rights reserved.