Zinc Oxide (ZnO) thin films were deposited on glass substrates via the ultrasonic spray pyrolysis technique. The films were subsequently annealed in ambient air from 350°C to 550°C for 3h. The morphology and structural properties of the thin films were studied by atomic force microscopy (AFM) and X-ray diffractometry (XRD) techniques. The X-ray diffraction studies revealed that the films are polycrystalline with the hexagonal structure and a preferred orientation along (002) directions. The optical properties of the films were characterized by UV-vis spectroscopy. The transmission values of the annealed ZnO films were average 80% within the visible range (400–700 nm). The optical band gap values of the films are between 3.27 and 3.23 eV. Electrical resistivity of the films was measured using four-probe measurement system. The electrical resistivity of the films decreased with the increasing annealing temperature. According to our investigation results, it can be seen that annealing treatment plays an important role on the some physical properties of ZnO films.