This park lies in the Solukhumbu and Sankhuwasabha districts of Eastern Nepal. Makalu - Barun is contiguous with Sagarmatha National Park in the West and to the North, with Qomolongma Nature Reserve in Tibet. This region comprise of several largely uninhabited watersheds most of which are drained by the Arun river. The world's fifth highest mountain (Makalu), one of the world's deepest river gorges (Arun) and the wild valley is an unique and relatively pristine ecosystem, enjoying a microclimate of extreme precipitation.

A series of distinct vegetation zones can be distinguished ranging from tropical Sal forest below 1000 m, through subtropical Schima - Castanopsis forest (1000 m - 2000 m), temperate evergreen oak and deciduous broad - leafed forest (2000 m - 3000 m), Sub-alpine fir and birch forests (3000 m - 4000 m), to alpine Juniper - Rhododendron scrub and pastures (4000 m -5000 m). Over 3000 species of flowering plants, 25 varieties of rhododendron, 48 primrose species, 47 orchid species, 19 bamboo species, 15 oak species, 86 species of fodder tree and 67 species of economical valuable medicinal and aromatic plants have been recorded from the park.

Some 25 species of mammal are found in this park including Red Panda, Snow leopard, Himalayan Thar, Himalayan Black Bear, etc.

Forests in the Barun valley are among the most important for birds in Nepal. Till now 400 species recorded from the park, out of them more than 300 are breeding species. Birds including dark-side thrush, Slaty-bellied Tesia, Broad-billed warbler, Spotted wren-babbler and Coral-billed scimitar-babbler.