ZnO thin films were deposited on a glass substrate by dc (direct current) and rf (radio frequency) magnetron sputtering. Post-deposition annealing was performed in different atmospheres and at different temperatures. The correlation of the annealing conditions with the microstructure and properties of the ZnO films were investigated by ultraviolet-visible spectroscopy, X-ray diffraction, conductivity measurement and scanning electron microscopy. Only the strong 002peak could be observed by X-ray diffraction. The post-deposition annealing of ZnO films was found to alter the film’s microstructure and properties, including crystallinity, porosity, grain size, intal stress level and resistivity. It was also found that after annealing, the conductivity of poorly conductive samples often improved. However, annealing does not improve the conductivity of samples with high conductivity prior to annealing. The resistivity of as-grown films annealing on the conductivity of ZnO, it is believed that annealing may alter the presence and distribution of oxygen defects, reduce the lattice stress, cause diffusion, grain coarsening and recrystallization. Annealing will reduce the density of grain boundaries in less dense films,which may decrease the resistivity of the films. On the other hand, annealing may also increase the porosity of thin films, leading to an increase in resistivity.