Acteonellids were one of the most significant groups of marine macro-invertebrates in the Late Cretaceous biota of the Tethyan Realm. They were common faunal elements associated with Cretaceous carbonate platform communities most notable for their abundance of rudist frameworks and thrived in coeval lagoons. The Upper Cretaceous fossil-bearing Karababa Formation, cropping out in southeastern Turkey, yields a remarkable assemblage of acteonellid gastropods and rudists. Cretaceous gastropods from sedimentary successions in Turkey barely have been studied over the past 80 years. The subgenus Trochactaeon, a very successful and widespread taxon of heterobranch gastropods within the family Acteonellidae, dominated acteonellid assemblages throughout the Late Cretaceous. In the present work, we present the first record of Trochactaeon (Trochactaeon) giganteus subglobosus from Turkey. It is from a single lower Campanian bed in the upper part of the Karababa Formation of the Gölbaşı region (south of Adıyaman), corresponding to the northwestern part of the Arabian Platform. This record complements information on the temporal and spatial distribution of Trochactaeon at the southern margin of the Tethyan Ocean during the last part of the Cretaceous Period. This discovery increases the documented diversity of the paleofauna from the Upper Cretaceous succession in southeastern Turkey and provides new insights into the paleoenvironment of the carbonate ramp of the northern Arabian plate, and the paleobiogeography of Campanian gastropods in general.