Abstract: A large-scale investigation of surface sediments was carried out off the Yellow River mouth and in the nearby Bohai Sea during August-September 2007. Approximately 250 samples were selected to determine CaO and smectite content using X-ray fluorescence spectrometry and X-ray diffraction. The analyzed data show that the CaO content distribution has similar occurrence to the smectite, which decreases seaward gradually from the Yellow River mouth. The study area can be classified into three provinces in terms of CaO and smectite contents. Provinces Ⅰfrom the river mouth to the central part of Laizhou Bay, is characterized by high contents of CaO and smectite,>7.30% and >12.3% respectively. In contrast, the contents of CaO and smectite are as low as <5.62% and <10.8% in province Ⅲ, which covers the eastern and southern Laizhou Bay. Province Ⅱ is distributed between provinces Ⅰand Ⅲ, where the contents of CaO and semctite range from 5.62% to 7.30% and from 10.8% to 12.3% respectively. The results demonstrate that the CaO and semctite contents in surface sediments of southern Bohai Sea can not only be used as indictors to trace the dispersion of the Yellow River sediments to the sea in the study area, but also has important implications of hydrodynamical conditions off the river mouth.