Arunachal Pradesh is home to a very rich mammalian wildlife population as the wide variety of altitudinal and climatic conditions have given rise to different forest types which create corresponding natural shelter , food etc. to varieties of wildlife. It has two National Parks and four Wildlife Sanctuaries. It is home to many rare and highly endangered species of Wild life like Mishmi, Takin, Hoolock Gibbon, Musk Deer, Bharal, Hisbid Hare, Flying Squirrel and more than 500 species of birds.

Namdapha National Park amongst them has perhaps the widest diversity of habitat of any of South Asia's protected areas. It is unique, with it's elevation varying between 200 to 4500 mts. and has all four large cats, the tiger, leopard, clouded leopard and snow leopard in addition to lesser feline species like the Golden cat and marbled cat.

Seven species of primates i.e. Hoolock Gibbon, Slow loris, Assamese macaque, Rhesus macaque, Pigtailed macaque, Stumptaile macaque and Capped langur are found here.

All the three goat antelopes found in India i.e. Serow, Goral and Takin are found here. Arunachal Pradesh is the only place in India where Takin is found. Among the large mammals, Mittan, which is a cross between the wild Gaur and domestic cattle, buffalo and elephant are all found in the plains and adjoining hills.

Arunachal Pradesh is perhaps the only State which has four major cats, i.e. tiger (Panthera tigris), leopard (Panthera pardus), clouded leopard (Neofelis nebulosa) and snow leopard (Panthera uncia). Lesser cats like the golden cat, leopard cat and the marbled cat are also found here.

Seven species of primates i.e. hoolock gibbon, slow loris, Assamese macaque, rhesus macaque, pig-tailed macaque, stump-tailed macaque, and capped langur also occur in the forests of the State. This is the only state where all the 3 goat antelopes occurring in India, i.e. serow, goral and takin are found. The highly endangered hispid hare (caprolagus hispidus) is also found in low grassy areas of the State.

Among the smaller mammals several Rodents (squirrel, porcupine and rats), Civets, mongoose, linsang, shrew and bat species are also to be found. On higher elevations, animals like goral, Himalayan black bear, red panda, are met with in various parts of the State. Over 500 bird species inhabit Arunachal Pradesh including some endangered and endemic ones like, white winged wood duck, Sclater’s Monal, Temmincks Tragopan, black necked crane, Mishmi wren and Bengal florican.

The 'Mithun' (Bos Frontails) exist both in wild and semi-domesticated form. This animal has religious significance and intimate relation with socio-cultural life of the people. Traditionally, the mithun is a unit of wealth and is allowed to move freely in jungle till it is either used for food on festive occasions and marriage feasts, or for barter.

More than five hundred bird species have been recorded in Arunachal Pradesh, many of which are highly endangered and restricted to this state , e.g. White winged wood duck, sclater monal, temminck's tragopan, Bangal florican etc. This state has the highest number of species of pheasants with some ten species at different altitudinal levels. Arunachal Pradesh is equally rich in reptiles, amphibia and pisces. Pythons and snakes of all colours and descriptions are found in the forests all almost all the levels upto the temperate zone.

The invertebrate faunal communities are found in the dense and evergreen forests of Arunachal Pradesh. Numerous species of butterflies, moths, beetles and all other kinds of small creatures make Arunachal Pradesh a paradise for Entomologists and Naturalists.

Arunachal also has more than 500 rare species of Orchids.