Radiolarian fossil analyses were conducted to determine the depositional age of the Izumi Group, eastern Shikoku. Fourteen of total 19 samples yielded radiolarian fossils. Most samples contain Dictyomitra koslovae and Amphipyndax tylotus, and do not include Clathrocyclas tintinnaeformis, Myllocercion acineton, or Clathrocyclas gravis. Those assemblages can be correlated with the Amphipyndax tylotus assemblage zone of Yamasaki (1987), the Amphipyndax tylotus interval zone of Hollis and Kimura (2001), and the Archaeodictyomitra lamellicostata zone of Hashimoto et al. (2015). Therefore, the depositional age of the Izumi Group in this district is estimated to be early Late Campanian, Late Cretaceous.