The southern mountain cavy (Microcavia australis) is a species of South American rodent in the family Caviidae.

Southern mountain cavies are tailless rodents with short, speckled, greyish-yellow fur, fading to pale grey on the underparts.

They are found across almost the whole of western and southern Argentina, where they inhabit arid and semiarid lowlands, often close to rivers or in areas dominated by thorn bushes.

[1] Three subspecies are currently recognised:[2] Southern mountain cavies eat leaves, fruits and other plant material, with mesquite and Capparis being reported as particularly common foods.

[2] Natural predators include owls, hawks, grisons, foxes, and skunks, and southern mountain cavies alert one another of danger with low-pitched alarm calls.