Abstarct: Here in this work we have studied the gas (O2 and CO2) sensing properties of SnO2 thin films which are grown by spray pyrolysis method. Through this research we have studied several parameters such as: substrate temperature, the volume of sprayed solution, annealing process and presence of impurities (here Co atoms) on the crystal structure and surface morphology of the laxyer which in turn affect on the gas sensing of the device. For structural properties, surface morphology and thickness of the laxyers we have used the X-ray diffractometer (XRD), scanning electron microscope (SEM), and UV-Vis. spectrometer. According to experimental results we found that a number of parameters including the size and preferential crystallite direction, also surface grain morphology have crucial influences on the sensitivity of the device.