Components of clay mineral in the sediments of different regions of the Bohai Sea are much the same. The main clay mineral is illite; chlorite, kaolinite and montmorillonite are less but palygorskite-sepiolite are scarce. From the component, the crystallinity and the distribution of clay mineral in the Bohai Sea, it is shown that they are not controled by sedimentary enveroment but depend on the component of sediment and clay mineral of denudation area, as well as on the hydrodynamic condition of the Bohai Sea. Based on the changes of the clay mineral component and of the chemical element content,the Bohai Sea may be divided into two regions of clay mineral component,the boundary of which lies from the estuary of Luanhe River to the town of Penglai. 1. Illite-kaolinite-chlorite mineral region, which is located in the south part of the Bohai Sea (in Bohai Bay and. Laizhou Bay). This region was mainly affected by the Huanghe River (Yellow River ) and partly by Lanhe River. 2. Illite-chlorite-kaolinite-montmorillonite region, which is located north part of the Bohai Sea (in the Liaodong Bay).