Abstract New fossil marsupials from Paleogene levels at Antofagasta de la Sierra, in Northwestern Argentina, are described: Punadolops nov. gen. (Prepidolopidae), represented by a single species, P. alonsoi ( Pascual , 1983 ), Bonapartherium serrensis nov. sp. (Bonapartheriidae), and an isolated lower molar tentatively assigned to Arminiheringia sp. (Proborhyaenidae). Marsupials from Antofagasta de la Sierra show only minor differences with respect to other Paleogene marsupial assemblages from Northwestern Argentina. On the contrary, all of them markedly differ with Patagonian marsupials of equivalent age. A review of the mammalian taxa recovered at this locality, together with its stratigraphic situation, led us to tentatively assign these levels to a Mustersan (Middle Eocene) age.