In this work optical, electrical, structural and surface properties of polycrystalline ZnO thin films grown from aqueous solutions (with pH = 5) have been reported. The films have been deposited on glass substrates by ultrasonic spray pyrolysis technique at a substrate temperature of 350 ± 5 °C. Zinc acetate dissolved in deionized water has been used as starting solution. The ZnO thin films have been annealed in air at 450 and 500 °C to improve their physical characteristics. X-ray diffraction reveals that the films are polycrystalline in nature having zincite type crystal structure. Electrical resistivity values of the films have been increased after annealing process. Films are highly transparent in the visible region. The dependence of refractive index, n, and extinction coefficient, k, on the wavelength for ZnO films has been also reported. Optical band gap values have been determined using optical method. Finally, it has been concluded that annealing temperature has an important effect on the optical, structural, surface and electrical properties of the deposited films.