Viscacha rats are a group of rodents in the family Octodontidae. All species are found in Argentina. They are placed in the following genera:
- Genus Octomys
- O. mimax , mountain viscacha rat, found in the Andes
- Genus Pipanacoctomys
- P. aureus, the golden viscacha rat, found near a salt flat
- Genus Tympanoctomys (4 species, 3 extant), found in desert shrubland near salt flats
- T. barrerae, the plains viscacha rat
- T. kirchnerorum, Kirchner's viscacha rat,
- T. loschalchalerosorum, the Chalchalero viscacha rat
- †T. cordubensis