By employing zinc acetate and sodium hydroxide as raw materials, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the reaction temperature, the OH-/Zn2+ mol ratio and the reaction time on the morphologies of the ZnO powders were discussed. The reaction conditions were obtained, under which the ZnO of flower-like particles, micro-rods and flake particles was synthesized, respectively. The crystal structures and morphologies of those ZnO particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZnO with flower-like structures was composed of lots of micro-rods with hexagon morphology. The XRD patterns indicated that the ZnO powders were hexagonal wurtzite structures with high purity. Finally, the growth mechanism of the ZnO particles was discussed. By employing zinc acetate and sodium hydroxide as raw materials, ultrafine ZnO powders with different morphologies were synthesized synthetically through hydrothermal method. The influences of the reaction temperature, the OH- / Zn2 + mol ratio and the reaction time on the morphologies of the ZnO powders were discussed. The reaction conditions were obtained, under which the ZnO of flower-like particles, micro-rods and flake particles were synthesized, respectively. The crystal structures and morphologies of ZnO particles were characterized by X-ray diffraction (XRD) The ZnO with flower-like structures was composed of lots of micro-rods with hexagon morphology. The XRD patterns indicated that the ZnO powders were hexagonal wurtzite structures with high purity. Finally, the growth mechanism of the ZnO particles was discussed.