In the present paper, different types of metal doped ceria CeO2-MOx (M = Sc, Y, Dy, Zr and Hf) with fluorite structure have been prepared with a complex polymerization method. The O-2-releasing potential of prepared samples was evaluated at 1500 degrees C for a two-step water splitting process. The partially oxygen defected CeO2-MO1.5 (M = Sc3+, Y3+ or Dy3+) mixed oxide exhibited an enhancement of the O-2 evolution on CeO2-ScO1.5 owing to the crystal-chemical effect that cation with smaller ionic radius (Sc3+) compensates the volume expansion of crystal lattice resulted in the reduction of Ce4+ with smaller ionic radius into Ce3+ with larger ionic radius. The CeO2-MO2 (M = Zr4+ and Hf4+) produced larger amount of O-2 than that for CeO2-MO1.5 mixed oxides, since CeO2-MO2 has no oxygen vacancy initially. While the ionic radii of Zr4+ and Hf4+ are almost equal, the higher O-2-releasing reactivity of Ce0.9Hf0.1O2 than that of Ce0.9Zr0.1O2 is explained in terms of ionicity of M-O bond. Also, the weight losses of CeO2, Ce0.9Zr0.1O2 and Ce0.9Hf0.1O2 in the mitigation process from high Po-2(O-2 gas stream) to low Po-2 (Ar gas stream) atmosphere were determined. The quasi activation energies in the initial period of the O-2-release for CeO2, Ce0.9Zr0.1O2 and Ce0.9Hf0.1O2 were evaluated 105, 84.2 and 75.0 kJ/mol, respectively. The O-2-releasing reactivity is considered from the standpoint of an activation energy. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.