A template-free sot-gel chelating method was developed to synthesize a hierarchical layer-stacking CeO2 nanostructure. The morphologies of the as-prepared CeO2 were spindle-like and flower-like particles which were both assembled by many porous nano-flakes. The basic unit, nano-flake, was organized by numerous nanoparticles with a size of 10 nm while the porous structure was formed. The as-prepared CeO2 exhibited a high surface area of 171.6 m(2) g(-1), high pore volume of 0.31 cm(-3) g(-1) and narrow pore size of 4.0 nm. Compared to the commercial CeO2, this novel structure showed much higher activity for CO oxidation which can be ascribed to its higher surface area, small crystal size and novel hierarchical porous structure.