Radiolarian fossils have been newly discovered from the uppermost part (Koyamada Formation) of the Somanakamura Group in the eastern marginal zone of the Abukuma Mountains, northeast Japan. The radiolarian fauna contains Pseudodictyomitra sp. cf. P. carpatica (Lozyniak), Sethocapsa sp. cf. S. kaminogoensis Aita, Hemicryptocapsa capita Tan Sin Hok, and so on. This association indicates an early Early Cretaceous age. The age assignment is consistent with that by ammonites (Berriasian).