Abstract: Based on the clay mineral contents from 187 stations in the surface sediments,this paper deals with the assemblages and the distributions of clay minerals in the surface sediments off the Yangtze River estuary. The research results show that illite dominates the surface sediments off the Yangtze River estuary with the smectite or kaolinite the second and chlorite the lowest;the illite-smectite-kaolinete-chlorite-assemblage is the main type of the clay minerals assemblage in the area,with the illite-kaolinete-chlorite-smectite-type as the second;the source of clay mineral is mainly from the Yellow River and the Yangtze River. The Q-type cluster analysis shows that sediments from both the recent and ancient Yellow River were deposited mainly in the northeast part of the study area to the north of 29°30'N. Substance from the Yangtze River were deposited mainly in the western and middle parts off the Yangtze River estuary.