ODP Leg 184 Site 1148 recovered up to 859 m deepsea sediments spanning the fast 32.8 Ma from the northern South China Sea (SCS), which is the longest record known so far in recording the detail evolutionary history of the SCS since the Oligocene. Geochemical analysis reveal that the SCS has undergone complicated sedimentary and tectonic evolutionary processes. The composition of the sediments had obvious changes or discontinuities at 32 Ma, 30 Ma, 28.5 Ma, 25 Ma, 23.5 Ma, 16 Ma, 10 Ma, 8 Ma and 3 Ma, respectively, reflecting tectonic or environmental turning points. Especially, the great discontinuous change in the sediment composition at the Oligocene/Miocene boundary with slumps and sedimentation breaks indicates a period of important tectonic activities in the SCS and Eastern China areas. This tectonic event played a key role in the transforming of many sediments basins in the Eastern China from graben basins to downwarped basins, as well as in the formation of the general topographic character in the region.