| Name of the Candidate | Party Name | Result |
| RAM PRIT PASWAN | Bharatiya Janata Party | 71614 |
| RAMAWATAR PASWAN | Rashtriya Janata Dal | 65372 |
| MAHESWAR RAM | Bahujan Samaj Party | 2650 |
| RAKESH KUMAR | Independent | 2271 |
| VISHNATH PASWAN | Independent | 2029 |
| UTIM PASWAN | Communist Party of India (Marxist-Leninist) (Liberation) | 1945 |
| PAWAS KUMAR PASWAN | Samajwadi Party | 1349 |
| CHHEDI RAM | Independent | 1181 |
| RAM CHANDRA MANDAL | National Jagaran Party | 1055 |
| SIYARAM SADAY | Samajwadi Janata Dal Democratic | 1025 |
| UMESH PASWAN | Akhil Bhartiya Mithila Party | 967 |
| None of the Above | None of the Above | 3447 |
| AC No | Category | Poll Phases | Last Date of Nominations | Date of Polls | Result |
| 37 | SC | Phase V | Oct 8th 2015 | Nov 5th 2015 | Nov 8th 2015 |
Rajnagar is in Madhubani district and comprises of Andhratharhi and Rajnagar community development blocks. The Rajnagar assembly constituency is a part of the Jhanjharpur Lok Sabha constituency. There are 2,72,110 eligible voters in the Rajnagar constituency of whom 1,44,831 men and 1,27,268 women.
One of the nine assembly segments located in the Madhubani district of Bihar, Rajnagar assembly constituency is currently being represented by Rama Watar Paswan who won the seat for the Rahstirya Janata Dal (RJD) by defeating his nearest BJP rival Ramprit Paswan by a margin of 15,742 votes in a bypoll held on 21st August in 2014, necessitated due to the resignation of its sitting RJD MLA Ram Lakhan Ram Raman from the seat.
Ram Lakhan Ram Raman was earler elected from the Khajauli assembly constituency in 2000, 1995 and 1980. While his win in 2000 came as an RJD nominee, he was elected as a CPI candidate in 1995 and 1980. Ram Lakhan Ram Raman was former Bihar secondary and higher education minister.
Out of the Bihar's ten assembly seats that went to the polls in the bye-elections which took place after the Lok Sabha elections in 2014, the BJP won 4, whereas the RJD and the JD (U) was victorious on 3 and 2 seats respectively. The Congress won one seat.
In the last general assembly polls to the Bihar legislative assembly held in 2010, Rajnagar was won by Ram Lakhan Ram Raman who had defeated Ramprit Paswan by a margin of 2459 votes. In that election, whereas Ram Lakhan Ram Raman polled 40584 votes, Ramprit Paswan received 38125 votes and was distantly followed by Ram Ekwal Paswan with 13367 votes.
In 2010 the JD (U) went to the polls in alliance with the BJP. However, as things stand today, the BJP and the JD (U) have parted ways and the Lok Janashakti Party (LJP), the ally of the RJD in the last assembly elections, is now a part of the BJP led NDA. The JD (U), the RJD and the Congress have joined forces to fight the BJP.
Reserved for the candidates belonging to the scheduled castes, Rajnagar came into being before the last general assembly elections in Bihar in 2010.
Located in the north Bihar's Mithila region, Rajnagar is one of the six assembly constituencies that unite to create the parliamentary constituency of Jhanjharpur which is currently represented by Birendra Kumar Chaudhary of the BJP who won it by defeating his nearest rival and sitting MP and RJD candidate Mangani Lal Mandal in the last Lok Sabha general elections in 2014
Sitting MLA Ramawatar Paswan of RJD will take on Ram Preet Paswan of BJP in Rajnagar. Both the candidates faced each other in the August 2014 bypoll and are ready to face each other in a tough poll battle. This time RJD MLA may find it tough to retain his seat as people want change and are swayed by the rising popularity of PM Modi in Bihar. The sitting MLA of the Rajnagar segment is Ramwatar Paswan of RJD who defeated BJP's Ram Preet Paswan in the byelections held in 2014.
Ramwatar Paswan bagged 58,495 votes against Ram Preet Paswan's 55,047 votes. The Rajnagar constituency is reserved for Scheduled Caste candidates. The Rajnagar assembly segment was re-constituted in 2008 after the implementation of the orders of the Delimitation Commission of India. Rajnagar is in Madhubani district of the state.