Nano-sized cerium oxide particles in the size range of 5 to 500nm have been synthesized for use in chemical mechanical planarization (CMP) applications. The CeO2 particles were prepared using cerium nitrate salts with bases such as ammonium water, ethylamine, or other alkylamine /polyalkylamine compounds. Other additives such as urea can be added to affect crystallization and size growth of the final particles. The particle sizes of the resulting CeO2 particles depend on the initial concentrations of cerium salts, additive concentration, and solution pH. Reaction duration seems to have little effect on CeO2 particle sizes. Temperature effects on size were moderate. These CeO2 particles showed excellent surface quality and desirable polishing rate during CMP tests.