Two new species of gastropods belonging to the volutid genus Adelomelon Dall, 1906 are described from Tertiary strata of Patagonia, Argentina. Adelomelon posei n. sp. was found in the lower part of the Gran Bajo del Gualicho Formation (Río Negro Province), which is currently dated as Late Eocene through Middle Miocene in age. Adelomelon valdesiense n. sp. comes from the Puerto Madryn Formation (Chubut Province) of early Late Miocene age. Both species are characterized by angulated biconical teleodonch whorls and strongly developed rows of axial nodes, similar in shape to those of some Recent species of Adelomelon, but positioned differently. Discovery of two new species of the genus Adelomelon in the Tertiary of Patagonia significantly extends the known stratigraphic range of this genus from Late Eocene(?)—Miocene to Recent.