Neogene deposits distributed in five individual areas along the east coast of South Korea are all included in the Pohang Basin. The Pohang area is the largest and the sediments are divided into two groups. The lower, the Yangbug Group, consists of terrestrial deposits, while the upper, the Yeonil Group, composed mainly of marine deposits with an abundant marine fauna, includes five formations. The Yeonil Group is divided into three foraminiferal zonules, six molluscan assemblages, four diatom subzones, two silicoflagellate subzones and three nannofossil subzones. The age of the Yeonil Group is middle Miocene, when a cold current predominated with occasional warm incursions. Correlation of sediments between Pohang and the other areas is discussed. Pliocene deposits are only present near Seoguipo City on Jeju Island (Cheju Do). The Seoguipo Formation is more likely to be Pliocene in age (Blow's N.19–N.21 Zone), and was deposited in the littoral zone of a warm open sea.