The Chitwan Valley (Nepali: चितवन उपत्यका) is an Inner Terai valley in the south of Nepal, encompassing the districts of Makwanpur, Chitwan and Nawalpur. The valley is part of the Terai-Duar savanna and grasslands ecoregion of about 150 km (93 mi) length and 30–48 km (19–30 mi) width.
Major cities are Hetauda and Ratnanagar in the easternmost part of the valley, Narayangarh and Bharatpur in its central part.
The Chitwan Valley is drained by the East Rapti River, which flows from the eastern Mahabharat Range into the valley near Hetauda, where it turns west and flows along the axis of the valley. About 20 km (12 mi) west of Hetauda the Rapti meets the eastern border of Chitwan National Park. For the next 70 km (43 mi) it forms a natural boundary between human settlements on its right-hand side and protected area on its left-hand side. West of Meghauli it joins the Narayani River, a Ganges tributary called Gandaki River in India.