We describe in detail the calcareous nannofossil assemblages present in the uppermost Cenozoic sequences in the southern Kwanto region, Japan and in the Vrica section (the Pliocene/Pleistocene boundary stratotype), southern Italy. Ten of twelve calcareous nannofossil biohorizons previously recognized in the Quaternary sequences in the Northeast Atlantic Ocean (TAKAYAMA and SATO, 1987) also occur in these areas. These datums allow us to correlate the uppermost Cenozoic sequences in the southern Kwanto region with these sequences along the Japan Sea margins. We clarify the relationships between the calcareous nannofossil biohorizons and the benthonic foraminiferal zones recognized in the sedimentary basins along the coastal regions of the Japan Sea. We also clarify the relation between these biohorizons and the Pliocene/Pleistocene boundary at its stratotype. The first occurrence of Gephyrocapsa caribbeanica, which occurs seventeen meters above the Pliocene /Pleistocene boundary and thirty meters above the Olduvai event at the Vrica section, is usable as the excellent indicator to detect the Pliocene/Pleistocene boundary.
