Abstarct: In this thesis, SnO2 and Indium doped SnO2 thin films with different atomic percentages (0%, 2.5%, 5%, 10% and 15%) were synthesized on glass substrates by sol-gel dip-coating method and the effects of annealing time, annealing temperature and In doping on the structural and optical properties of the films were investigated. To characterize the structure of the films, the X-ray diffraction measurements and Raman spectroscopy to investigate, the surface morphology of the samples the FESEM device, the composition of the samples the EDAX device and for the optical properties of the samples, UV-Vis spectrophotometer in the Wavelength rang of 300-1100 nm were used. Analysis of the X-ray data of SnO2 showed that increasing the annealing time from 1-3 hours improves the crystalline quality of the samples, and at 3 hours annealing time, the tetragonal rutile structure is formed. Band gap values decrease slightly with increase in annealing time. The X-ray spectra of the annealed samples at 400,450 and 500 0C showed formation of the pure SnO2 phase with increase in annealing temperature. FESEM images of the samples showed that the uniformity of the annealed film at 450 0C would be better than other samples. The average transmittance of all samples is more than 85%, and the band gap values of the samples slightly increased with increase in the annealing temperature. The X-ray spectra of the indium doped samples showed the formation of the tetragonal rutile structure of SnO2. The optical study of the samples revealed that the average transmittance decreases with doping and the band gap values of the samples also decreased with increasing indium impurity.