The Chilinidae comprises 16 species currently cited for Argentina, mostly distributed in Patagonia. All original descriptions of these species have been based on shell characters, and their internal anatomy is poorly known. Here a new species, Chilina iguazuensis, is described, including shell, radula, and reproductive and nervous systems. This species, found in Iguazú National Park, Misiones Province, Argentina, in the Upper Iguazú River rapids, has the following distinctive characteristics: aperture length equal to last whorl length; central radular tooth asymmetric and bicuspid, with both cusps serrated; and prepuce length 60% of penis sheath length. Chilina iguazuensis is endemic in Iguazú National Park, along with Chilina megastoma, which inhabits waterfalls in the same river.