Under the parliament's rules of procedure, Nikolic's resignation was noted without debate. The current speaker, Milutin Mrkonjic of the Socialist Party, said the session would continue on Monday.
The session is expected to continue with a debate on a bill on ministries, to which more than 90 amendments have been submitted, after which a new government is to be elected.
The deadline for the election of the country's new government expires at midnight on Tuesday.
As he previously announced in the media, Nikolic resigned after the parliament completed a discussion on his replacement and before it put the matter to the vote.
Addressing the parliament, Nikolic repeated that the leader of the Democratic Party of Serbia and incumbent PM, Vojislav Kostunica, had asked him to assume the post of parliament speaker because "he was afraid that (Democratic Party leader Boris) Tadic would betray him".
Nikolic went on to say that "Serbia will lose Kosovo to the European Union, while Russia will defend it, and Serbia will again be put to the test. The Radicals will opt for Russia and lead the nation into battle... If the government calmly accepts Kosovo's being taken away, the Radicals won't. There will be no peace in Serbia."
During the debate which preceded Nikolic's resignation, deputy speaker Natasa Jovanovic of the Radical Party strongly criticised "the Ustasha Croatian Radio and Television" for making a special program on the crisis in Serbia, which included a television vote on how much Nikolic poses a threat to the Balkans.
Jovanovic also criticised the leader of the Liberal Democratic Party, Cedomir Jovanovic, for taking part in the program.