Ceria–based precursors doped with calcium, calcium–samarium and calcium–gadolinium were prepared by an improved homogeneous precipitation method using ammonium oxalate as precipitant, high purity reagents Ce(NO₃)₃·6H₂O, Ca(NO₃)₂·4H₂O, Sm₂O₃ and Gd₂O₃ were used as raw materials, urea was used as pH adjuster of the mixed solution. The as–synthesized precursor were calcined at 700 ℃ for 4.5 h. The calcined powders were characterized by X–ray diffraction (XRD), scanning electron microscopy(SEM), and Brunauer–Emmett–Teller(BET) specific surface area measurements. The results show that the calcined powders have satisfactory characterizations when the initial hydrolysis pH is approximately 1, the total concentration of mixed cation ions is 0.5 mol/L, and the initial concentration of precipitant is 0.05 mol/L. The powders after calcined have a single cubic fluorite crystalline structure and higher phase purity, with spherical nano–sized particles about 34–39nm in diameter and narrow size distribution. In this study, doped ceria precursors were redispersed and washed in ethanol can alleviate the degree of agglomeration of the calcined powders.