Highly uniform Ce(OH)CO3 flowers were successfully prepared in large quantities using a facile hydrothermal approach from the reaction of Ce(NH4)(NO3)4 with CO(NH2)2 at 160℃ in a water-N2H4 complex. The influences of the N2H4 content and temperature on flower formation were discussed. CeO2 flowers were prepared by thermal conversion of Ce(OH)CO3 flowers at 500 ℃ in air. Both Ce(OH)CO3 and CeO2 flowers were characterized by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The UV-vis adsorption spectrum of the CeO2 flowers showed that the band gap energy (Eg) is 2.66 eV, which is lower than that of bulk ceria.