Situated in Gangetic plains bio-geographic zone of the country, the forest has combination of bhabar and terai tracts.

It enters in India at Valmikinagar, where two rivulets Sonha and Pachnad joins it, forming a holy confluence ‘Triveni’.

The Botanical Survey of India has categorized seven vegetation types within the limits of the national park: The important tree species are sal (Shorea robusta), karam (Adina cardifolia), asan (Terminalia tomentosa), bahera (Terminalia bellirica), asidh (Lagestromia parviflora), simal (Salmelia malaberica) and satsal (Dalbergia latifolia).

In hilly regions, piyar (Buchanania lanzan), mandar (Dillenia aurea), banjan (Anogeissus latifolia), bhelwa (Semecarpus anacardium), harra (Terminalia chebula), bodera (Eugenia operculata) occur.

[5] The reptiles in Valmiki National Park are pythons, king cobra, banded krait and sand boa.

[4] At present 241 bird species have been reported to be present in Valmiki National Park, including kalij pheasant, quail, paradise flycatcher, grey shrike, tree pipit, white-eyed warbler, green barbet, waders, ibises, storks, pitta, plovers, snipes, Oriental pied hornbill, white-eared night heron, emerald dove, several owls, spotted owlet and nightjars.