A total of 79 species of benthic foraminifera belonging to 49 genera and 60 species of diatoms belonging to 35 genera are identified from the core samples of the deltaic sediments in Nagdong Estuary. On the basis of benthic foraminiferal fauna and diatom flora, the deltaic sediments of the cores can be divided into three environmental intervals : the upper Interval I bay environment ; the middle Interval II offshore bay environment ; the lower Interval III is bay environment. The sea-water had advanced into Nagdong Estuary already earlier than 7133 yr.B.P. This marine transgression may be correlated with the Jomon Transgression in the Japanese Islands. Sea-level fluctuation occurred after around 7000 yr.B.P., which might be due to the vertical movement of the land of Nagdong Estuary.