Indium tin oxide (ITO) thin films have been deposited onto quartz glass substrates by a sol-gel process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. 0-20% by weight Sn-doped indium oxide (ITO) films were prepared by heat-treatment at above 400 degreesC. The electrical, optical and structural properties of ITO thin films were investigated. The thickness of ITO film was measured by ellipsometer. The electrical resistivity was measured by using four-point probe method. The ITO thin films containing 10 wt.% Sn showed the minimum resistivity of rho = 1.5 x 10(-3) Omega -cm. The spectral transmittance of ITO thin films was measured in the wavelength range from 275 to 900 nm by a UV-vis spectrometer. The film has high transmittance above 80% and has an absorption edge at 300 nm. X-Ray diffraction measurements employing CuK alpha radiation were performed to determine the crystallinity of the ITO films which showed that the ITO films were polycrystalline with a cubic bixbyite structure. XRD results show that a single phase is detected for In-Sn or;ide and X-ray photoelectron spectroscopy (XPS) results show that a single valence state and chemical bonding state is observed for In and Sn in In-Sn oxides. Therefore, we can say that Sn is incorporated into the In2O3 structure substitutionally.