Highly oriented polycrystalline ZnO films have been prepared by rf actively sputtering technique. We have investigated the structural and optical properties of ZnO films. x-ray diffraction was employed to analyze the influence of the post-treatment on the properties of ZnO thin films. The grain size increases with annealing temperature. The shift of the diffraction peak position from its normal powder value was observed. The photoluminescence (PL) spectra of these samples consist of one emission peak centred at 2.9eV.The intensities of PL peaks decrease with increasing annealing temperature. We propose that the emission comes from the interstitial Zn.