Cerium oxide nanoparticles were produced by laser ablation in an aqueous solution. Submicron-sized cerium oxide particles were size-reduced by pulsed-laser irradiation into those having diameters of 3.6 nm. It was found that the bandgap of the nanoparticle was larger and the Ce3+ concentration within it was higher than those prepared by other conventional methods. These characteristic structures are likely to originate from additional defect sites in the nanoparticles produced by laser ablation, where O-2 ions have a lower coordination with Ce ions, resulting in removal of O atoms and reduction of Ce4+ into Ce3+. (C) 2014 Elsevier B. V. All rights reserved.