Abstarct: In this thesis the morphological, structural and optical properties of molybdenum trioxide (MoO3) thin films synthesized using spray pyrolysis and hydrothermal methods and molybdenum disulfid (MoS2) samples prepared using hydrothermal methods were studied.Then, the gas sensing application of MoO3 thin films prepared by pyrolysis spray was investigated. XRD pattern analysis of MoO3 thin films synthesized by pyrolysis spray method with various carrier gas pressures showed the formation of thermodynamically α-MoO3 phase with orthorhombic crystalline structure. The band gap decreased with increasing the carrier gas pressure. In order to growth of MoO3 thin films, the effects of substrate type, reaction temperature and pH of precursor solution were studied. All samples synthesized by hydrothermal method showed the formation of mextastable h-MoO3 phase with hexagonal crystalline structure. In the investigating the effect of temperature on the growth of thin films, a phase change from orthorhombic to hexagonal was observed as the reaction temperature was increased. Also, band gap decreased with increasing the reaction temperature. For samples prepared using different seed laxyers, the band gap was decreased and it was increased for samples prepared by different pH of precursor solutions. FESEM images of samples showed the formation of well shaped hexagonal microrods. For MoS2 samples prepared by hydrothermal method, the effect of reaction time was investigated. XRD pattern analysis showed the formation of hexagonal phase of MoS2. SEM results showed that the obtained MoS2 nanofloweres are comprised of very thin nanosheets with the thickness of about 20-40 nm. Finally, the sensing properties of samples prepared by spray pyrolysis toward ethanol at different temperatures were studied. Results showed that the optimum operating temperature was 200◦C and sample prepared under the carrier gas pressure of 1.8 bar shows the maximum sensing response.