Abstract: Grain size analysis is a tool widely applied in sediment classification and environmental interpretation. There occur sand, silt, silty sand and sandy silt in the areas of eastern Bohai and northern Yellow seas, with a few gravelly sediments. The spatial distribution of sediments shows a W-E zonation of grain size, roughly parallel to the coast lines. They are coarser in northern area and finer along southern area in general, and become finer along the direction from the coast to the sea. The grain size distribution pattern depends upon the factors of provenance, seabed topography and ocean circulation. According to the seabed deposits, 6 depositional areas can be identified, including the areas of the Laotieshan Channel-Liaodong-Bozhong tidal sandy deposits, the Shandong Peninsula coastal muddy deposits, the Central North Yellow Sea muddy deposits, the Central South Yellow Sea muddy deposits, the West Korean Gulf tidal sand ridge deposits and the Central Bohai Sea muddy deposits. All of the sedimentary environments of the depositional areas are discussed in details in the paper.