The Jurassic organicrich mudstone source rock in the northern Qaidam Basin occurred mainly in lacustrine and deltaic sedimentary environments. This paper focuses on the characters of biomarrker composition in these two different environments and thus seven typical samples were collected from the two settings for this purpose. The results indicate that the distribution and composition of the three kinds of compounds are very different, especially the distribution of tricyclic terpane, abundance of diahopanes, and a relative composition of regular sterrane. The composition of regular sterane suggests the different times, while distribution pattern of tricyclic terpane and abundance of diahopanes indicate the discrepancies of sedimentary environments. In deltaic source rocks, distribution of tricyclic terpane follows the order of C19>C20>C21, with a relatively high abundance of diahopanes. In contrast, in lacustrine source rocks, the distribution of tricyclic terpane shows C19