Nanocrystalline ceria (CeO(2)) particles have been successfully prepared by microwave-assisted heating technique from an aqueous solution containing ammonium Ce(IV) nitrate and sodium hydroxide. Further thermal treatment of the as-prepared powder at 500 degrees C resulted in the formation of the well-crystallized CeO(2) nanoparticles with an average crystal size of about 8 nm, varying with the heating temperature. The as-prepared powder and the CeO(2) nanoparticles were examined using X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. It was found that the morphologies of the synthesized powder show from rod-like for the as-prepared sample to sphere-like for the heat-treated nanoparticles. Mechanism of CeO(2) nanocrystallite growth during annealing is primarily investigated. (C) 2005 Elsevier Ltd. All rights reserved.