The Mountain Hawk-eagle is a medium-large raptor at about 70–72 cm in length. The typical adult has brown upperparts and pale underparts, with barring on the undersides of the flight feathers and tail. The breast and belly and underwing coverts are heavily streaked. The wings are broad with a curved trailing edge, and are held in a shallow V in flight. Sexes are similar, but young birds are often whiter-headed.
The Sri Lankan and south Indian subspecies (S. n. kelaarti) is smaller and has unstreaked buff underwing coverts. A 2008 study based on the geographic isolation and differences in call suggest that this be treated as a full species, Nisaetus kelaarti. The Japanese subspecies N. n. orientalis is larger, lighter, and has only a very small crest, which is large in the other two subspecies.
The heavier underpart streaking and wing shape help to distinguish this species from the similar Changeable Hawk-eagle.
It is a bird of mountain woodland, which builds a stick nest in a tree and lays usually a single egg. Mountain Hawk-eagles eat small mammals, birds and reptiles.
