ZnO thin films were deposited on Si(400) substrates by e-beam evaporation technique, and then post-annealed at different annealing temperatures (200-800°C). Dependence of the crystallographic structure, nano-strain, chemical composition and surface physical Morphology of these layers on annealing temperature were studied. The crystallographic structure of films was studied using X-Ray Diffraction (XRD) method, while the chemical composition and surface morphology of layers were investigated by Field Emission Scanning Electron Microscopy (FESEM). The XRD results showed that ZnO (002) crystallographic orientation was a preferred orientation for growth of ZnO thin films. Increasing of annealing temperature caused increasing of intensity and decreasing of FWHM for ZnO (002) peak and decreasing of dislocation density in the films. The nano-structural investigations also showed that mentioned peak position and nano-strain were varied with increasing of annealing temperature. Chemical composition analysis showed that the ratio of oxygen to Zinc increased with increasing of annealing temperature. SEM images showed a mixed structure of nanowires and nanosheets for annealed films at 350 and 500°C, and a granular structure for annealed samples at 200 and 800°C. However, the annealed films at the highest temperature (800°C) had a dense structure and larger grains than the annealed film at 200°C temperature.