Ceria (CeO2,) nanoparticles of 10-30 nm in average particle size have been synthesized via electrochemical deposition method in cerium(III) chloride solution with an undivided cell as electrochemical cell and ethanol-acetyl acetone as additives. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR) and thermal analysis (TG-DTA) are introduced to characterize the samples. The results indicate that the as-prepared powders after being treated at 650 degrees C are nanocrystalline with the cubic fluorite structure and the sphericity in shape. It is revealed that the size of ceria nanoparticles can be decreased effectively by adding the ethanol-acetylacetone solution. In addition, the possible formed mechanism of CeO2 nanometer-scale powder. The role of additive is also investigated in this paper. (c) 2007 Published by Elsevier Ltd.