Abstarct: The reaction and high response of nanostructures oxide S.C. (such as Zinc-Oxide and Tin-Oxide) to varicose gases leads to application of these materials in gas sensor which have been used science and technology. So many investigations are done to synthesis and growth of these nanostructures by experimental and Semi-industrial methods. The main purpose of this thesis is synthesis and structural studies of ZnO nanostructures for usage in gas sensors. These nanostructures have mainly synthesized by CVD direct Oxidation method. Various ZnO nanostructures have been synthesized by Spray, PVD, CVD methods at different conditions. The structural studies show formation of ZnO nanostructures such as nanowires, nanorods and nanoflowers which their lengths are less than few microns and their diameter are about 30-80 nm. In some samples the nanostructures has formed in coral-sand shapes. The samples exhibit optical excitation in various wavelengths spacially in violet-blue, green and Infra-red region. The optical excitation shows low intensity in green region but high intensity in violet-blue region. Gas sensing measurements with different samples and conditions exhibit that the grown samples on Al2O3 substrate show the best sensitivity compaire to the others.