Ce0.88Mn0.12Oy and CeO2 nanoparticles have been successfully prepared via a supercritical antisolvent process. High-resolution transmission electron microscopy displays the hollow and spherical structures of these nanoparticles. X-ray diffraction analysis demonstrates the formation of Ce0.88Mn0.12Oy solid solution. N-2 adsorption reveals that the Ce0.88Mn0.12Oy has nearly the same surface area with the CeO2. It is shown that the Ce0.88Mn0.12Oy has higher oxygen storage capacity (OSC) than the CeO2. To understand the mechanism of the improved OSC of the Mn doped CeO2, Raman spectroscopy, X-ray photoelectron spectra and density functional theoretical (OFT) calculations have been performed. It is found that the Ce0.88Mn0.12Oy presents more oxygen vacancies, indicating the easier of oxygen mobility from bulk to surface. DFT calculations reveal that structural and electronic modifications are caused by the incorporation of Mn in the CeO2, resulting in activated oxygen species. The oxygen vacancy formation energy is lowered by the Mn doping. These changes are responsible for the enhanced OSC of the Ce0.88Mn0.12Oy. (C) 2012 Elsevier Ltd. All rights reserved.