A planktonic foraminiferal census, benthic foraminiferal delta (super 18) O and magnetostratigraphy were used to determine the Pliocene/Pleistocene boundary in deep-sea sediments at ODP Site 1148 in the South China Sea, and compared with the P/P boundary stratotype in Vrica, Italy. The P/P boundary between MIS 64 and 65 is located at a depth of 112.75 m and dated to be 1.805 Ma at Site 1148, which coincides stratigraphically with the P/P boundary of the Vrica stratotype. A change in coiling from sinistral to dextral in Pulleniatina obliquiloculata is found in MIS 62 and dated to be 1.76 Ma. This event, together with the top boundary of the Olduvai subchron, may be the most reliable datum nearest the P/P boundary in the South China Sea. Except for these datum levels, there is no significant biostratigraphic event or environmental change found at or near the P/P boundary at Site 1148. In comparison, a rapid increase in benthic delta (super 18) O occurred between 3.05 and 2.53 Ma with a 5 degrees decrease in winter SST at Site 1148, indicating the formation of the Northern Hemisphere Ice Sheet.