Sonpur Assembly constituency, often spelt Sonepur, is in Saran district in the Indian state of Bihar.

[1] Ram Sundar Das, sitting MLA from Sonpur 1977–1980, served as Bihar's Chief Minister briefly in 1979.

As per Delimitation of Parliamentary and Assembly constituencies Order, 2008, No.

20 Saran (Lok Sabha constituency).

[2] It was earlier part of Chapra (Lok Sabha constituency).