After more than 15 hours of debating, MPs elected Nikolic, deputy to ICTY indictee Vojislav Seselj.
A total of 142 of 250 deputies voted for Nikolic - Radical deputies, representatives of Prime Minister Vojislav Kostunica's Democratic Party and the Socialist Party - while 99 voted against.
The other candidate, democrat Milana Milosevic, received votes from Boris Tadic's Democratic Party, G17-Plus, Cedo Jovanovic's Liberals, Nenad Canak's League of Vojvodina Social Democrats and minority representatives.
The new Serbian parliament was constituted on 14 February and under the constitution the government must be constituted by 14 May at the latest or the parliament will be dissolved and new elections called..
So far, all attempts to form a ruling coalition have failed.