Zinc oxide thin films were prepared by sol gel method and spin coating technique, using zinc acetate as precursor solution on glass substrate. The prepared films were annealed at three different temperatures to study the effect of annealing on the structural and optical properties of ZnO thin films. The deposited and annealed films were characterized by X-ray diffraction (XRD), UV-Vis-NIR spectroscopy and scanning electron microscopy (SEM) coupled with microanalysis (EDX). The XRD pattern shows that ZnO films are polycrystalline in nature and crystallite size increases with the increase in annealing temperature. Optical transmittance measurements were taken using UV-Vis-NIR spectrophotometer and the calculated values of the direct band gap energy, Eg was between 3, 28 and 3, 42 eV.