Fluvio-lacustrine deposits of the Tsubusagawa Formation occupy a small area on northern Kyushu Island. Although many important vertebrate fossils have been recovered from this formation, its detailed ...depositional age has not been accurately determined. In this study, we present data on the petrographic properties and chemical composition of tephra beds from the Tsubusagawa Formation and similar aged beds from the Mizazaki Group, with the aim of correlating tephra beds. The Miyazaki Groupcrops out in southeastern Kyushu and is an important Pliocene series on the island. Our study showed that the “Mori 1” and “Tanokuchi” tephra beds of the Tsubusagawa Formation are correlated with the NKT-2 and NKT-13 tephra beds of the Miyazaki Group, respectively. Based on these correlations, the depositional age of the stratigraphically lowest horizon of the Tsubusagawa Formation is estimated to be 3.5Ma.