Abstarct: In this experimental thesis the surface morphology, structure and optical properties of tungsten oxide (WO3) thin films without doping and doped with tin (Sn) were studied. In order to grow thin films two techniques of spray pyrolysis and hydrothermal were used. Structural, optical, and morphological properties of samples were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) pattern analysis, and UV-Vis spectroscopy. In spray pyrolysis method the effect of doping with Sn in different atomic ratio (0, 1, 2, 5 and 10%) was investigated. FESEM images of samples show the formation of the nested circular rings with a many nanoparticles on the surface of thin films, which by increasing the amount of dopant, the number, size and the shape of the nanoparticles change. X-ray diffraction pattern analysis for the undoped sample of WO3 shows the peaks of hexagonal crystal structure of WO3 and tetragonal crystal structure of W5O14, so that with increasing the dopant concentration to 2 at.% a change in crystal phase was observed from hexagonal to orthorhombic phase. For the samples grown by hydrothermal technique also the effect of doping with Sn in different atomic ratio (0, 1, 2, 5 and 10%) was studied. The XRD pattern analysis shows the formation of hexagonal WO3 and orthorhombic WO3.H2O crystal structures for undoped sample, and hexagonal and orthorhombic WO3 and tetragonal H0.23. WO3 structures for doped samples. FESEM images showed the growth of entangled nano-sheets for undoped sample and the formation of spheres on the surface of doped samples. Using transmission and reflection spectrum of thin films, optical transmittance (at the wavelength of 550 nm), and the direct band gap of samples were obtained and analyzed. In this thesis, gas sensing properties of samples towards different concentrations of ethanol was measured using the samples prepared by spray pyrolysis. Measurements was conducted at two temperatures of 200 °C and 250 °C. The highest response belongs to the sample doped with 10 at.% Sn measured at 250 °C, which is 98% for 1000 ppm of ethanol.