The size-controlled ceria nanospheres have successfully synthesized via a simple solvothermal treatment by employing the mixtures of water and diethylene glycol as the reaction solvent with the aid of polyvinylpyrrolidone. The properties of the ceria nanospheres were characterized. The synthesis parameters were investigated in detail by a series of control experiments. It is found that the surfactant species and reaction solvents were the crucial factors determining the formation of ceria nanospheres, and the size of ceria nanospheres can be controlled by adjusting the reaction temperature and time. The noble metal coated ceria nanospheres shows the excellent catalytic activity in the conversion of carbon monoxide, and especially for Au coated ceria nanospheres, the T-50, where 50% CO was converted to CO2, can reach to 62.0 degrees C. (C) 2010 Elsevier B.V. All rights reserved.