Mahnar is an assembly constituency in Vaishali district in the Indian state of Bihar.

129 Mahnar Assembly constituency is composed of the following: Mahnar community development block; Borhan urf Rasulpur Gaus, Basantpur, Mohiuddinpur Garahi, Harprasad, Mahipura, Sohrathi, Mahisaur, Chandsarai, Dihbuchauli, Peerapur, Rasalpur Purushottam, Bishunpur Bedauliya, Saiyad Mahammad urf Salha, Khopi, Arniyan, Hazrat Jandaha, Bahsi Saidpur, Mukundpur Bhath and Loma gram panchayats of Jandaha community development block.

Rama Kishore Singh of LJP defeated Munshilal Rai of RJD in October 2005 and February 2005.

Muneshwar Prasad Singh of JP defeated Akhilesh Kumar Ray of Congress in 1977.

In the elections to Mahnar constituency in 2015 Umesh Kushwaha of JD (U) defeated Achyutanand Singh with a large margin of 27000 votes.