A vast area of primary tropical forest dominated by two spectacular extinct volcanoes, Kahuzi and Biega, the park has a diverse and abundant fauna. One of the last groups of eastern lowland (graueri) gorillas (consisting of only some 250 individuals) lives at between 2,100 and 2,400 m above sea-level.
Straddling the Albertine Rift and the Congo Basin, Kahuzi-Biega National Park is an exceptional habitat for the protection of the rainforest and the eastern lowland gorillas, Gorilla berengei graueri. Extending over 600,000 ha, are dense lowland rainforests as
well as Afro-montane forests, with bamboo forests and some small areas of sub-alpine prairies and heather on Mounts Kahuzi (3,308 m) and Biega (2,790 m).
The Park contains a flora and fauna of exceptional diversity, making it one of the most important sites in the Rift Albertine Valley, it is also one of the ecologically richest regions of Africa and worldwide. In particular, the most important world population of eastern lowland gorillas (or de Grauer), sub-species endemic to the Democratic Republic of the Congo (DRC) and listed under the endangered category on the IUCN Red Data Book, uses the mosaic of habitats found in the property.