ABSTRACT: The Nummulites amakusensis Yabe and Hanzawa– N. junbarensis Matsumaru – N. hongoensis Hanzawa – Discocyclina pratti (Michelin) Assemblage (generic term: Amakusa Assemblage) zone of lower Eocene (Ypresian)/middle Eocene (Lutetian), assigned to Letter Stage a2 and the P9 planktonic foraminifera zone in the Philippine Archipelago, is recognized in 20 stratigraphically positioned samples from the Akashimisaki Formation in the Amakusa Islands, Kyushu district Japan, and also in three samples from the Tachien and Meichi Sandstones, Hsuehshan Range, central Taiwan, based on age diagnostic larger foraminifera of five genera and 15 species, together with associated planktonic foraminifera. At the Bozubana locality (station No. 3), Amakusa Islands, unusual white clastic limestone layers in fault blocks of theAkashimisaki Formation yield reworked late Paleocene (Thanetian) larger foraminifera and Late Cretaceous (Maastrichtian) planktonic foraminifera in the Bozubana Thrust Fault zone, which was activated by the Peri Tunghai Tectonic Movement in the Ryukyu Arc after the Eocene formations were deposited. The Amakusa Assemblage is proposed for a key regional framework in the eastern Tethys indicating the late Early Eocene (Ypresian)/early Middle Eocene (Lutetian) based on zone P9 and Letter Stage a2.