Nathnagar Assembly constituency is one of 243 constituencies of legislative assembly of Bihar.

It comes under Bhagalpur Lok Sabha constituency along with other assembly constituencies viz.

Gopalpur, Pirpainti, Kahalgaon, Bhagalpur and Bihpur.

[1] Nathnagar comprises CD Blocks Nathnagar & Sabour; Gram Panchayats Puraini North, Puraini South, Baluachak Puraini, Sanholi, Baijani, Khiribandh, Jamani, Saino, Bhawanipur Desri, Chandapur, Jagdishpur, Sonuchak-Puraini, Imampur, Shajangi cense town & Habibpur Nagar Panchayat of Jagdishpur CD Block.

[2] ^by-election