Abstract: The dark mudstone from Jiufotang and Yixian formations in X-D1 well of Xiushui Basin, northern Liaoning Province, is evaluated in terms of organic matter abundance, type and maturity based on the organic geochemical data such as organic carbon and pyrolysis. The results show that the mudstone of Jiufotang Formation is between immature and low mature stage; while that of the Yixian Formation, low to mature stage. The mudstone from upper Yixian Formation is medium-good source rock of Ⅱ1-Ⅱ2 types of organic matter, which provides basic data for further oil-gas exploration in Xiushui Basin.