Two new species of Odontostomidae are described from Argentina: Clessinia juramentoensis sp. nov. (near Juramento river, Metán Political Department, Salta province) and Clessinia subcylindrica sp. nov. (from Chancani, Pocho Political Department, Córdoba province). Both species are compared with all the species of Clessinia represented in Argentina; images of the related species are presented. C. juramentoensis is characterised by its sub-pyriform shell, small, lustrous to naked eye; secondary ureter opening between the middle and the distal area of the lung roof; penis inner wall with penial area IV occupying 1/3 of penis total length. C. subcylindrica is characterised by its small sub-cylindrical-globose shell, penial area II sculptured with numerous, long, strongly contracted lamellae, penial area III with a pilaster formed of a single fold, much contracted, becoming scalloped. The purpose of this study is to provide complete data on shell morphology and internal anatomy, as well as the distributional information on both species.