Nanocrystalline Tin oxide thin films of multiple layers were successfully prepared by the sol-gel method. Spin coater have been used to deposit the films. The starting material is SnCl21. The SnO2 material was characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and EDS analysis. The optical properties (A, T, R) of the SnO2 thin film of various annealing temperatures (400,500,600 Co) and the electrical properties have been studied. Characterization results indicated that the products are composed of crystalline SnO2 nanoparticles which exhibit the cassiterite-type tetragonal crystal structure3. SEM revealed that with increase annealing temperature, the uniformity of the film increased. The variations of the refractive index (n), extinction coefficient (K) and Optical Conductivity with the wavelength have been studied. Nevertheless, the variation of the optical band gap with film thicknesses shows a significantly decrease in the values of the band gap with increase the film thicknesses. SnO2 was tested as a gas sensor to detect carbon dioxide (CO2) gas. It shows high sensitivity for various concentrations of CO2 gas2.