Planktonic foraminifers from Site C0001, drilled during Integrated Ocean Drilling Program Expedition 315 off the Kumano region in the northwestern Pacific Ocean, were examined to establish a reference biostratigraphy of the Nankai Trough Seismogenic Zone. Planktonic foraminifers are present throughout the cores at this site, with the exception of several barren intervals in the lower part of the section. Seventeen biohorizons are recognized at this site. Among these, 15 biohorizons were refined and 2 biohorizons were detected after the onboard study. The studied sequence correlates with Zones N.17b–N.22, ranging in age from late Miocene to Holocene. A new age-depth plot for the site is proposed based the foraminiferal data from this study combined with nannofossil biohorizons determined on board during the expedition.