Stratigraphic horizon of the Km3 tephra layer intercalated in the lower part of the Kitaura Formation, Akita Prefecture, Japan, is located above the calcareous nannofossil datum plane 11 (1.65Ma). The Km3 tephra layer, approximately 1m thick, is mainly composed of volcanic glass shards with minor amounts of plagioclase, quartz and biotite. On the basis of the stratigraphic position, lithofacies, petrographic characteristics and chemical composition of glass shards, the Km3 tephra layer is correlated to the Om-SK110 Tephra (1.65Ma). By this result, it is clarified that the Km3 tephra layer was transported more than 450km away from its probable volcanic center situated in the Hida Mountain Ranges, central Honshu Island.