Abstract: The content and composition of clay minerals from 83 surface samples in the Sanmen Bay were analyzed with XRD. Through grain size trends analysis and clay minerals assemblages characteristics of related rivers, the provenance of clay minerals and sediments resources of the Sanmen Bay were discussed. The results show that the majority of clay mineral in surface sediment in Sanmen Bay are illite, followed by kaolinite and chlorite, and the minority is smectite. The higher abundance of illite is distributed in the middle of the Sanmen Bay, and the higher kaolinite and chlorite located at the upper bay area either near the river estuaries or bay branches, and smectite displayed patchy distributions along the coast. The surface sediment in Sanmen Bay mainly comes from the Changjiang River, while sediments from small local mountainous rivers only affect the estuary area.