Sarairanjan is a town in the Sarairanjan (Vidhan Sabha constituency) in Samastipur district in the Indian state of Bihar

As per Delimitation of Parliamentary and Assembly constituencies Order, 2008, No. 136 Sarairanjan Assembly constituency is composed of the following: Sarairanjan and Vidyapati Nagar community development blocks.

Sarairanjan Assembly constituency is part of No. 22 Ujiarpur (Lok Sabha constituency).

It is located on the musrigharari - Vidyapati Nagar road. Public transport(tempos) are available to nearest town Dalsinghsarai, Mushrigharari and Vidyapati Nagar. It is located approximately 6 km south of Musrigharari.

Sarairanjan market is the main market for all the nearby villages in the constituency. It has a government hospital, a police station Block and water department near to the market. Nearest railway station is samastipur jn. approx 13 km.