Abstract: A process of microwave-hydrothermal method was established to synthesize ZnO nanopowders，using zinc chloride and sodium hydroxide as raw materials.Besides，the particle size，morphology，and purity of the prepared product were characterized by X-ray diffraction（XRD） and transmission electron microscope（TEM）.The influences of reaction temperature，microwave  radiation period，microwave power，and concentration ratio of Zn2+ to OH- on yield and size of ZnO nanopowders were investigated by single factor experiments and the optimum preparation conditions were obtained by orthogonal experiments.Experiment results indicated that: under the temperature of 120 ℃，c（Zn2+）∶c（OH-）=1∶1.2，microwave radiation period of 10 min，and microwave power of 500 W，nano-sized ZnO with an average size of 70 nm，belonging to hexagonal system，could be produced and the yield reached 93.5%.Moreover，the crystallite sizes of the prepared samples were mostly uniform with narrow size distribution.

Key words: nano-sized ZnO, microwave-hydrothermal method, preparation