Abstract: After the crude oil of low-middle maturity, which generated and accumu-lated in situ, was found in the carbonate source bed of the Lower Qinglong Formation (T₁X), Jurong Basin of Jiangsu,immature carbonate source rocks are also found in Upper Qinglong Formation(T₁s). Such a discovery of immature carbonate source rocks in Lower Triassic, which relatively is rather old in geological time, is the first time in China, and it merits geologists attention. Analytical data of the composition of hydrocardon compounds, pyrolysis GC of rocks, GC of alkanes, IR of kerogens, and R° are used to reveal the geochemical characteristics of the immature carbonate source rocks and the geological origin.