Abstarct: In recent years, the use of resistive gas sensors to monitor and investigate qualitatively and quantitatively environmental factors such as gases in the environment has been the focus of researchers; Therefore, the technology related to gas sensors, which is considered one of the environmental monitoring tools, is widely developing and improving. These sensors are used in various industries, mines, medicine, environment and various research fields, with the aim of identifying gaseous compounds. Gas sensors that are used in the real environment should have features such as high sensitivity and accuracy, selectivity, response time and short recovery time, repeatability, stability, and appropriate detection limit. Other important features are of special interest in the commercialization process of gas sensors, such as: low cost for manufacturing and production, small dimensions of sensors, especially for their use in wearable sensors, low energy consumption of parts, easy manufacturing and simple equipment for their production. . The above cases have caused that gas sensors baxsed on nanostructured mextal oxides have attracted a lot of attention from researchers and so far, many researches have been carried out with the approach of improving the performance of resistive gas sensors. Some of the researches conducted in this field are baxsed on the use of composite materials, catalyst, ultraviolet light radiation with the aim of providing activation energy and use of new methods in the construction of parts, etc. Despite the outstanding features of gas sensors baxsed on mextal oxides, there are also weaknesses in them that have limited their commercialization process and widespread use in the real environment. One of the most important weaknesses is the limited gas selectivity in the sensing process of these parts. Among the various mextal oxides that have been introduced by researchers to detect gases, compounds such as ZnO and SnO2 have received special attention from researchers. The purpose of this research is to investigate and study the gas sensing process with the help of ZnO and SnO2 nanocomposite compounds in order to improve the performance of the gas sensor and strengthen the gas selectivity. baxsed on this, various combinations of pure and composite materials of ZnO and SnO2 nanostructures were synthesized and several sensor parts were made baxsed on these materials. Then the manufactured parts were used for sensing different gases. In this thesis, the process of synthesis of nano materials and nano composites of ZnO and SnO2, manufacturing of sensor parts and sensing of different gases with the help of manufactured parts have been discussed and investigated. The results of this research show that some of the challenges in mextal oxide gas sensors can be overcome by using SnO2/ZnO nanocomposite compounds. The most important results obtained from this research in the use of SnO2/ZnO nanocomposite are the reduction of the operating temperature of the sensors, the possibility of replacing thermal stimulation with ultraviolet radiation stimulation, achieving fast sensors with a significant reduction in response time, and the existence of a suitable calibration curve. Due to the good linear relationship between the response of the sensors and the concentration of the target gas. The results of this research show that nanocomposite sensors have a good potential for commercialization.