More than 10 000 m thick marine strata have been recorded in the Yinggehai-Qiongdongnan Basin of the northern South China Sea since Oligocene. Twenty-four planktonic foraminiferal zones are renewed based on the analysis of abundant micropaleontological data in study area, together with recent progress of ODP Leg 184 and the international standard chronostratigraphic timescale (2004). The ages of the Yacheng Formation, Lingshui Formation, Sanya Formation, Meishan Formation, Yinggehai Formation, Ledong Formation are discussed in this paper.