Sn doped zinc oxide polycrystalline thin films were prepared by sol-gel process. The sol was prepared from zinc acetate dehydrate and tin chloride were used. 2-methoxyethanol and monoethanolamine were used as the solvent and stabilizer, respectively. The quantity of tin in the sol was 0, 15, and 25 at.% Sn with annealing temperature 400, 500 and 600°C. Structural investigation including surface morphology and microstructure was carried out by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The films give a hexagonal wurtzite structure with diffraction peaks at (100), (002) and (101). Changes in particle size with an increase in annealing temperature were observed in the SEM micrograph. The optical properties were determined by photoluminescence (PL) and UV-Visible (UV-VIS-NIR) spectrometer. The band gaps increased (2.78 eV to 4.10 eV) as the concentration of Sn was increased and the increasing of annealing temperature. Annealing temperature plays a key role in the formation of defects which is strongly related to the nonradiative recombination centers. The increment of the band gap is acceptable as a requirement for good anti-reflecting coating element. Therefore, these films can be applied on silicon solar cells.