CeOsub.2 is an important rare earth (RE) oxide and has served as a typical oxygen storage material in practical applications. In the present study, the oxygen storage capacity (OSC) of CeOsub.2 was enhanced by doping with other rare earth ions (RE, RE = Yb, Y, Sm and La). A series of Undoped and RE–doped CeOsub.2 with different doping levels were synthesized using a solvothermal method following a subsequent calcination process, in which just Ce(NOsub.3)sub.3∙6Hsub.2O, RE(NOsub.3)sub.3∙nHsub.2O, ethylene glycol and water were used as raw materials. Surprisingly, the Undoped CeOsub.2 was proved to be a porous material with a multilayered special morphology without any additional templates in this work. The lattice parameters of CeOsub.2 were refined by the least–squares method with highly pure NaCl as the internal standard for peak position calibrations, and the solubility limits of RE ions into CeOsub.2 were determined; the amounts of reducible–reoxidizable Cesup.n+ ions were estimated by fitting the Ce 3d core–levels XPS spectra; the non–stoichiometric oxygen vacancy (Vsub.O) defects of CeOsub.2 were analyzed qualitatively and quantitatively by O 1s XPS fitting and Raman scattering; and the OSC was quantified by the amount of Hsub.2 consumption per gram of CeOsub.2 based on hydrogen temperature programmed reduction (Hsub.2–TPR) measurements. The maximum OSC of CeOsub.2 appeared at 5 mol.% Yb–, 4 mol.% Y–, 4 mol.% Sm– and 7 mol.% La–doping with the values of 0.444, 0.387, 0.352 and 0.380 mmol Hsub.2/g by an increase of 93.04, 68.26, 53.04 and 65.22%. Moreover, the dominant factor for promoting the OSC of RE–doped CeOsub.2 was analyzed.