ABSTRACT: To study the Neoflabellina bioevents, 132 samples were collected from the middle of the Abderaz Formation (24-m-long), in the Kopeh-Dagh Basin, Iran. The studied interval represents the lower part of the Dicarinella asymetrica zone placed in the uppermost Coniacian and lower Santonian. The presence of Neoflabellinids was recorded in the interval considered here in the following six geological sections: Shorab, Padeha village, Muzduran, Abderaz village, Qarehso, and Hajgelichkhan. In the present study the inoceramid species Platyceramus undulatoplicatus (Roemer), which defines the Coniacian/Santonian (C/S) boundary, was not found. The occurrence of a Neoflabellinid bioevent with the First Occurrence Datum (FoD) of pillbox morphotypes, including Globotruncana linneiana and Dicarinella asymetrica, is considered to be a sufficient proxy for the C/S boundary. Four species of Neoflabellina were observed in this study: Neoflabellina praecursor, Neoflabellina gibbera, Neoflabellina praerugosa, and Neoflabellina suturalis, along with several indeterminate forms. Neoflabellina gibbera and Neoflabellina praecursor occur for the first time at the C/S boundary.