ZnO thin films were grown on glass slides by thermal evaporation of zinc powder in vacuum followed by heat treatment in air. The films were characterized by x-ray diffraction (xrd), Raman scattering and scanning electron microscopy (SEM). Xrd pattern for as-deposited thin film sample consists of hexagonal Zn structure with slight wurtzite ZnO texture. It is observed that the heat-treatment at between 450 and 600 degrees C for 1 to 3 h turns the xrd pattern almost completely to wurtzite ZnO structure. SEM micrographs display flakes like hexagonal button shaped grains for as-deposited thin film which turns to needle like nanometer size structures with heat treatment. The red shift of some vibrational modes in Raman spectra for as-deposited thin film relative to the heat treated films and the introduction of a line at around 582 cm(-1) indicate that ZnO thin films have defects such as oxygen vacancies or zinc interstitials. The most intense Raman mode due to high frequency oxygen vibration for as-deposited zinc film is red-shifted by about 7 cm(-1) relative to the Raman mode for the ZnO thin film heat-treated.