The parliamentary majority appointed Tomislav Nikolic, deputy head of the Serbian Radical Party, speaker of the Narodna Skupstina Tuesday.
"This choice casts doubt on society's further development and the opportunities to bring Serbian people's life into line with European standards," said Boris Tadic, leader of the Democratic Party, whose candidate lost the voting.
Nikolic was backed by the center-right Democratic Party of Serbia (DSS), led by outgoing Prime Minister Vojislav Kostunica, and the Communists.
Nikolic's election follows weeks of unsuccessful coalition talks between Tadic's Western-leaning Democratic Party and the DSS since the January 21 elections gave the victory to the Radicals but failed to produce an overwhelming majority.
The European Union repeatedly called for a union between the democratic parties fearing ultranationalists in power, and Enlargement Commissioner Olli Rehn called the signals from Belgrade "worrying".
May 14 is a deadline for forming a government in Serbia. Otherwise, new elections will be called in the country.
