This article reports a novel preparation of three-dimensional (3D) CeO2 originating from crystalline cerium formate by a surfactant-free route using H2O, ethanol and ethylene glycol as solvents. The sea urchin shaped 3D CeO2 gave rise to micro/nanocomposite structures with high BET surface area up to 234 m(2) g(-1). The 3D structure improved the reducibility of surface CeO2 due to the increased oxygen vacancy. Both 3D CeO2 and 5 wt% CuO loaded on 3D CeO2 exhibit high catalytic activities for CO conversion.