The park has a rich variety of flora and fauna and provides shelter to 1,178 plant species in the hilly region of the park and 349 species of birds inclusive of the Horn bills species, Trogons, Sunbirds and Ruwenzori Turacos.
The park’s swamps, bogs, marshland and riparian forests on hydromorphic ground at all altitudes are rare worldwide. The western lowland sector of the park is dominated by dense Guineo-Congolian wet equatorial rainforest, with an area of transition forest between 1,200 metres (3,900 ft) and 1,500 metres (4,900 ft).
The eastern hilly sector includes constant forest vegetation from 600 metres (2,000 ft) to over 2,600 metres (8,500 ft), and is one of the rare sites in Sub-Saharan Africa which reveals all stages of the low to highland transition, including six distinct primary vegetation types: swamp and peat bog, swamp forest, high-altitude rainforest, mountain rainforest, bamboo forest and subalpine heather.
Mountain and swamp forest grows between 2,000 metres (6,600 ft) and 2,400 metres (7,900 ft), bamboo forest grows between 2,350 metres (7,710 ft) and 2,600 metres (8,500 ft), and the summits of Mounts Kahuzi and Biéga above 2,600 metres (8,500 ft) have subalpine heather, dry savannah, and grasslands, as well as the endemic plant Senecio kahuzicus.
Amongst the 136 classes of mammals identified in the park, the eastern lowland gorilla is the most prominent. According to a 2008 status report of the DR of Congo, the park had 125 lowland gorillas, a marked reduction from the figure of 600 gorillas of the pre-1990’s battle era, and consequently the species has been listed in the endangered list. The park is the last refuge of this rare species. According to the census survey of eastern lowland gorillas reported by the Wildlife Conservation Society in April 2011, at least 181 gorillas were recorded in the park.
Other apes include the eastern chimpanzee, and several Cercopithecinae, Colobinae and owl-faced monkey. Some of the mammals include the bush elephant, bush buffalo, hylochere and bongo, Aquatic civet, eastern needle-clawed galago, Maclaud’s horseshoe bat, Ruwenzori least otter shrew, and Alexander’s bush.
The forest elephants are the largest mammals found in Kahuzi-Biega .it can be distinguished from other mammals by its height.