Sunsari District a part of Koshi Zone, is one of the seventy-five districts of Nepal, a landlocked country of South Asia. The district, with Inaruwa as its district headquarters, covers an area of 1,257 km² and at the 2011 census had a population of 763,487.

The area was originally part of Morang but became its own district in 1962 when Nepal was divided into 14 zones and 75 districts.

Major cities in Sunsari district are Inaruwa, Itahari and Dharan.