Abstract: Natural gas wells of Mandong area are located in Mandong, Longkou, Yingnan and Yingdong tectonic belts, having broad prospects for gas exploration. In this paper, the gas components carbon isotopic composition of the natural gas from Well Mandong 1, Well Longkou 1, Well Yingnan 2 and Well Yingdong 2 have been analyzed to discuss the genetic type of natural gas in this area. The results indicate that the natural gas from Well Mandong 1, Well Longkou 1 and Well Yingnan 2 has a few CO₂ and lot N₂, which is kerogen-cracking gas and typical wet gas. The natural gas from Well Yingdong 2 has a lot CO₂ more than other three wells, and has a few N₂, which is oil-cracking gas and belongs to a typical dry gas. The CO₂ and N₂ are organic origin. Natural gas of Mandong area is high and over matured marine sapropelic type gas. These findings will further guide the work of natural gas exploration in Tarim Basin.