Abstract: Zinc oxide (ZnO) hollow microspheres were prepared by coprecipitation with sodium citrate as surfactant. The microstructure and surface morphology of the samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). ZnO hollow sphere was applied on the gold finger electrode to form a humidity sensor. The DC resistance, AC capacitance and AC impedance of humidity sensor in different humidity environment were measured by the semiconductor tester Keithley 2400 and the high precision digital bridge TH2828. The results showed that with the increase of humidity, resistance of components was reduced, the AC capacitance and impedance increased (low frequency range).The complex impedance spectrum of ZnO hollow sphere in different humidity environment was detected. The equivalent circuit was given and its humidity sensitive mechanism was explained.