Wildlife ranges from mammals, birds, fishes, amphibians and reptiles to insects and other invertebrates. Some montane mammals such as pygmy squirrels and fruit bats are almost endemic to Kinabalu Park. Others like Thomas' Pygmy-squirrels, Black Shrews and Kinabalu Shrews are found nowhere else.

Of 29 bird species unique to Borneo, at least 17 are confined to the mountains, notably Kinabalu. These include subspecies of the Red breasted Tree-partridge and the Crimson-headed Wood-partridge. A common sight on the summit is the Mountain Blackbird. Kinabalu is home to over half of Borneo's 518 bird species, including Rhinoceros Hornbills.

Over 1,000 moth varieties, numerous small reptiles, insects and spiders are endemic to Kinabalu. Of the 900 known butterfly species in Borneo, some 600 are found here. Diversity - with over 100 species of mammals alone - does not guarantee sightings. Many animals are nocturnal or tree top dwellers. The most obvious are tree shrews and squirrels, of which 28 species are noted. Primates include Orang Utans, Borneon Gibbons, Leaf Monkeys, and two distinctive nocturnal species, the Slow loris and the Tarsier.