Abstract: The comprehensive research of the source rocks of the Lower Cretaceous in central sag of Bongor basin in Chad was conducted in this paper, based on the organic geochemical analysis data of the source rocks, from the aspects of source rock evaluation, history of the hydrocarbon generation and characteristics of the biomarkers, etc. The result indicates that the studied area is of characteristics of developed dark mudstone, high abundance of organic matter, good source rocks, Ⅱ1 organic matter type, effective source rocks dominated by K formation and its below M and P formations, and maturity as the key controlling factor of effective source rocks. The result of the history simulation of hydrocarbon generation indicates that the source rocks of K, M and P formations even reach the peak stage of hydrocarbon generation in or earlier than the Late Cretaceous and have large potential of resources, and the secondary hydrocarbon generation is impossible. The biomarkers analysis shows that the source rock of K formation deposits in fresh water?weak salt water and weak oxidation?weak reduction lacustrine sedimentary environment, but there are some differences in different layers and structural locations