Based on stable isotopic analysis of more than 1000 samples of planktonic and benthic foraminifers from ODP Site 1148 in the northern South China Sea (SCS), oxygen isotope stratigraphy has been applied to the last 3 million years for the first time in the SCS. Furthermore, paleo-oceanographic changes in the northern SCS during the last 6 million years have also been unraveled. The benthic foraminiferal delta (super 18) O record shows that before -3.1 Ma, the SCS was much more influenced by the warm intermediate water of the Pacific. The remarkable decrease in the deep-water temperature of the SCS during the period of 3.1-2.5 Ma demonstrates the formation of the Northern Hemisphere ice sheet. However, several sea surface temperature (SST) reductions during the early and middle Pliocene, reflected by planktonic foraminiferal delta (super 18) O, might be related to the growth of the ice sheet in the Antarctic region. Only those stepwise and irreversible SST reductions during the period of -2.2-0.9 Ma could be related to the formation and growth of the Northern Hemisphere ice sheet.