Abstract: Through the analysis of thin section, X-ray diffraction (XRD) and Rock-Eval pyrolysis, the Paleocene mudstones in the Lishui Sag of the East China Sea Shelf Basin were classified into different lithofacies, of which the organic matter (OM) content and hydrocarbon generation potential were compared. The results show that the lithofacies of the Paleocene mudstones in the Lishui Sag can be divided into laminar mudstones, sandy-massive mudstones, and muddy-massive mudstones based on their sedimentary structure and XRD mineral composition. In the laminar mudstone, the mineral matrix lamina and organic lamina are interlayered and discontinuously distributed, the OM content and hydrocarbon potential are the largest among different lithofacies, and such mudstone is mainly distributed in the western Sub-sag with the most developed in the Yueguifeng Formation. The sandy-massive mudstone has a high content of felsic minerals (feldspar and quartz) with large particle size; the muddy-massive mudstone has a high content of clay minerals which are uniformly distributed; and the OM in both lithofacies is scattered in the mineral matrix in the form of organic particles, with low OM content and hydrocarbon potential. The sandy-massive mudstone is mainly developed in the Lingfeng and Mingyuefeng Formations of the whole sag, while the muddy-massive mudstone is mainly developed in the Yueguifeng Formation of the eastern Sub-sag. Furthermore, by comparing the OM content and hydrocarbon potential of the Paleocene source rocks in the Lishui Sag with the main source rocks that developed in the Paleocene land area and post-Eocene marine area in China's offshore with petroleum discoveries, it is found that the Paleocene source rocks in the Lishui Sag have relatively high OM content and hydrocarbon potential, which deserves to be continuously explored for oil and gas. Overall, the characteristics of OM content, hydrocarbon potential and their spatiotemporal distribution of mudstones with different lithofacies vary greatly in the Lishui Sag of the East China Sea Shelf Basin, and the in-depth understanding of source rocks in this region should focus on the laminar mudstone and the Yueguifeng Formation of the western Sub-sag, which is of great significance in guiding its exploration and development of hydrocarbons.