The Moscow City Court on Monday threw out a lawsuit filed by A Just Russia to annul the results of the 2009 City Duma elections on the grounds that city officials helped United Russia secure victory.
A Just Russia will appeal, Interfax reported.
The October 2009 elections were widely denounced as rigged, but Moscow courts have rejected 64 lawsuits against the results. President Dmitry Medvedev and Prime Minister Vladimir Putin have refused to intervene in the elections, which prompted a brief boycott of lawmakers in the State Duma, saying they were fair and any challenge should be addressed in court.
None of the lawsuits included "strong reasons to doubt the results of the vote," Vyacheslav Shulepin, a member of the city's elections committee, which is a defendant in A Just Russia's lawsuit, told Interfax earlier.
United Russia won 32 seats in the City Duma, while the Communist Party won the other three.
Three parties — United Russia, the Communists and Yabloko — had been represented in the old City Duma, and one of the three Yabloko members joined United Russia after the elections.
In late October, the court dropped former Mayor Yury Luzhkov from the list of defendants in A Just Russia's lawsuit.
Analysts say new Mayor Sergei Sobyanin was picked to ensure that United Russia gets strong support from Muscovites in the 2011 State Duma elections.