Sarlahi District (Nepali: सर्लाही) is one of the 8 districts of Madhesh Province of Nepal. It covers an area of 1,259 km2 (486 sq mi) and had a population of 635,701 in 2001 and 769,729 in 2011.
It is bordered to the west by the Bagmati River, to the east by Mahottari District, to the north by the Sivalik Hills, and to the south by Bihar State of India.

Generally, the people of Sarlahi believe that the name Sarlahi comes from the name of the Sarla Devi temple. The Sarla Devi temple is situated in Hempur village in the Sarlahi district. There is a belief that if someone goes to the temple at night with a light, then that person will die. For that reason, people still do not go at night to that temple with light. There are no residences around this temple.