The park covers 760 km2 (293 sq mi) of the Anosy mountain range, the southernmost spur of the Malagasy Highlands and contains the last humid rainforests in the southern part of Madagascar.

[1] Andohahela National Park is 40 kilometres (25 mi) north-west of Fort-Dauphin and at the southern end of the Malagasy Highlands.

The mountains form a natural barrier to the moist trade winds that blow from the east, causing on the eastern side a rainfall of 1,500–2,000 millimetres (59–79 in) per year that supports one of the few rainforests south of the Tropic of Capricorn.

At the western edge of the park, the rainfall is just 600–700 millimetres (24–28 in) per year and the resulting vegetation is a dry spiny forest characteristic of southern Madagascar.

[1] The variety of habitats within Andohahela is mirrored in the richness of species that are found there, and the park is the richest place in Madagascar for lemurs.