Abstract: The biologic-source constitution, sedimentary environment, maturity and oil-generating potential of organic matter in the Carboniferous carbonate rocks and mudstones of the South Qilian Basin is studied preliminarily by means of biomarker analysis technology combined with other geochemical data. The result reveals that the hydrocarbon source rocks were developed in marine reducing sedimentary environment, their organic mother material is mainly low-grade hydrobios mixed with high-grade plants, and the organic material includes humic-sapropel and sapropel two types. The source rocks have high enrichment of organic matter and higher maturity, and possess favorable conditions to form gas and oil.