Valmiki National Park is a national park and tiger reserve in the West Champaran District of Bihar, India covering 898.45 km (346.89 sq mi). It is the only national park in Bihar.

The extensive forest area of Valmikinagar (formally known as Bhainsa Lotan) was previously owned by the Bettiah Raj and Ramanagar Raj until the early 1950s. It was declared a Wildlife Sanctuary in 1978. Valmiki National Park was established in the year 1990. Total area of the park is about 335.65 Km2. Valmiki Wildlife Sanctuary and National Park is the 17th Tiger Reserve of the country. The Valmiki Tiger Reserve comprises the National Park and the Wildlife Sanctuary.

It is located in West Champaran which derives its name from two words, Champa and Aranya, meaning forest of Champa trees. Geographically, it is situated between 83°0 50′ and 84°0 10′ E longitude and between 27°0 10′ and 27°0 03′ N latitude. Total forest area comprises about 900 square kilometres (350 sq mi), out of which the Valmiki Wildlife Sanctuary is 880 square kilometres (340 sq mi) and spread of the National Park is about 335 square kilometres (129 sq mi) area. In the north, the protected areas are bordered by Nepal's Chitwan National Park while the Indian state Uttar Pradesh bounds the sanctuary from western side. Bihar Government is turning 800 hectares of forest in VTR into Grassland making it India's biggest grassland.

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The landscape of Valmiki National Park encompasses foothills of the Sivalik Hills with a mosaic of the cliffs, ridges and gorges, hills, streams and valleys; dense forests, open woodlands, grasslands, swamps and riverine fringe. Situated in Gangetic plains bio-geographic zone of the Country, the forest has combination of bhabar and terai tracts. Boulder and pebble deposits by the Himalayan rivers in foothills characterized the Bhabar tract while the finer sediments deposits feature Terai lands.

Someshwar Hill Range and Dun Hill system with knife-edge ridges and precipitous slopes, cliffs, spurs, gorges, narrow valleys.

Older alluvium with sandy soil with variegated clay and loose boulder deposits and artesian flows; lateritic formations on higher contours and newer Alluvium on southern parts with reissuing springs akin to artesian flows.

Criss-crossing and meandering rivers, streams and rivulets, man-made canals; swamps and grasslands are featured on these lands. River Gandak forms the western boundary of Valmiki wildlife sanctuary. It enters in India at Valmikinagar, where two rivulets Sonha and Pachnad joins it, forming a holy confluence ‘Triveni’. The river is called ‘Narayani’ in Nepal. Harha – Masan River system originates from the Valmiki Forests and forms Burhi Gandak River down south. River Pandai flows into Bihar (India) from Nepal in the eastern end of the Sanctuary and meets Masan. All these rivers with their precursor and tributaries namely Rohua, Kotrahia, Manor, Bhapsa, Koshil, Singha, Dhonghi, Ganguli, Dhoram are full of youth and verve. Their cascades in wanton and wayward playfulness while descending from hills ridges and gorges are enchanting. Meeting the planes they slowly mature to serene grandeur.