CeO2nano-sized crystalline powders were prepared by sol-gel combustion method from ammonium cerium nitrate and citric acid, and the dependences of the particle size of synthesized powder on the precursor gel were investigated. The precursor gels and the synthesized powders were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray scattering (XRD). The colloid particle with nanometer size was firstly observed by FE-SEM, and its size variation had the same tendency as that of CeO2powders with the varying of the ratio of metal ions to citric acid. Furthermore, the probable reasons for the effect of gel structure on properties of nano-sized ceria powders prepared by sol-gel combustion were explained.