In order to determine the age of the sedimentary hiatus in the South China Sea and its geological significance, the calcareous nannofossil biostratigraphy of ODP Site 1148 was studied. Detailed stratigraphic data on Late Oligocene-Early Miocene diagnostic species were obtained. The nannofossil zonation of this interval was subdivided and the Oligocene-Miocene boundary was further determined. Several upper Late Oligocene events were recognized, indicating a long-term sedimentary hiatus in the uppermost Upper Oligocene. The time span of the hiatus is estimated to be about 2.2 Ma, at least from 23.9 to 26.1 Ma. The lithological and geophysical data from Site 1148 indicate some abrupt sedimentary changes that occurred below and above the hiatus. This hiatus at Site 1148 was probably related to tectonic change, a major ridge jump during late Oligocene sea-floor spreading in the South China Sea.