The reserve covers significant portions of the Nimba Range, a geographically unique area with unusually rich flora and fauna, including exceptional numbers of single-site endemic species, such as Nimbaphrynoides (a genus of viviparous toads), the Nimba otter shrew, and multiple species of horseshoe bats.

Both reserves were combined to form one World Heritage Site in 1981 (Guinea) and 1982 (Côte d'Ivoire) because of its outstanding biodiversity and unique mosaic of tropical habitats.

[1] Iron-ore exploration for mining in the most vulnerable montane zone started in 1992, and the reserve has been listed as a World Heritage Site in danger since then.

The Nimba Range is a narrow ridge extending approximately 40 km long, with an orientation of northeast–southwest; it forms a part of the southern extent of the Guinea Highlands.

Other rare and endangered animals found within the reserve include the West African lion, pygmy hippopotamus, zebra duiker, and a population of western chimpanzee that use stones for tools.

Mount Nimba lies in a remote region along the tri-national border of Guinea, Côte d'Ivoire, and Liberia, far from their capital cities.