Abstract: Traditionally, the first appearance datum （FAD） of planktic foraminiferGloborotalia truncatulinoides has been widely used as a reliable indicator of thePliocene-Pleistocene （P-P） boundary in marine-deposited sequence. However, recentstudies indicate that this datum is diashronous, because the FADs of Gt.truncatulinoides in the Indo-Pacific betwseen about 15°S and 40° S is earlier （2.6～2.7MaB.P.） than that in the equatorial Pacific （2.OMaB.P.）. Moreover, the P-P boundarybased on the commonly accepted FAD （2.0 MaB. P.） of Gt. truncatulinoides isinconsistent with the boundary according to the FAD （1.67～l.70MaB. P.） ofcalcareous nannofossil Gephyrocapsa oceanica s.l. This inconsistency is remarkable inthe conti nental margin sequence where high sedimentation rate resulted in a largestratigraphic interval between the FADe of Gt. truncatulinoides and Gephyrocapsaoceanica s.1. For instances, the interval between these two FADs is about 500m and1 300m from two rapidly deposited sequences of Taiwan. In this study, wedemonstrate that in the western part of Erhjen-chi section of southwestern Taiwan, thelast coiling change （from sinistlal to dextral） in the tests of planktic foraminiferPulleniatina is almost coeval with the FAD of G. oceanica s. l. Therefore, thePulleniartina coiling change could be used as a very useful datum for the P-Pboundary in Planktic foraminiferal biostratigraphy.