Eocene ostracodes are described from the Japanese Islands for the first time. These ostracodes, from the Iojima Group in southwestern Japan, are represented by cosmopolitan and low- to midlatitudinal paleobiogeographic groups as well as an endemic group. Based on the distributions of selected genera, the ostracode fauna of the Iojima Group has tropical to subtropical affinities, affirming links with the Tethys Sea. Six species are described as new: Cytheropteron liue, Eopaijenborchella kamiyai, Eopaijenborchella okinoshimaensis, Ambtonia? matsubarai, Paracypris? kuritai, and Trachyleberis? funatsuensis.