139 Rosera Assembly constituency is composed of the following: Rosera community development block; Phulhara, Lilhaul, Singhia-I, Singhia-II, Singhia-III, Mahen, Wari, Nirpur Bhaririya, Bangarahta, Hardiya, Mahra and Keothar of gram panchayats of Singhia CD Block; Shankarpur, Jakhar Dharampur, Ghiwahi, Dasaut, Rahiar North, Rahiar South, Ballipur, Bandhar, Karain, Raniparti and Rajaur Rambhadrapur gram panchayats of Shivaji Nagar CD Block.

Dr. Ashok Kumar won the Rosera seat, defeating his rival Manju Hajari.

In the 2010 state assembly elections, Manju Hajari of BJP won the Rosera seat defeating her nearest rival Pitamber Paswan of RJD.

Gajendra Prasad Singh of RJD defeated Ashok Kumar of JD(U) in October 2005 and February 2005.

Ramashray Rai of Congress (I) defeated Ram Lakhan Singh of Janata Party (SC) in 1980.