Abstract: There were many disputes about the origin of gas in Kekeya region since the field has been found in 1977. This paper is mainly concentrated on the geochemical characteristics of gas in Kekeya field. The carbon isotopic value of natural gases in kekeya region are much heavier than that of other natural gases in Tarim basin which are mainly derived from lower Palaeozoic marine source rocks. This study elicits that gas in Kekeya region is mixed gas. The maturity of gas is estimated as 1.8%~2.2%, which are generated by Carboniferous-Permian source rocks. In addition, it may be mixed with the gas derived from 0.9%~1.2% Ro source rocks.