The Federal Registration Service said in its lawsuit that the number of party members and local branches fell short of legal requirements adopted in 2004.
"The court ruled to grant the service's request and close the Republican Party," the court ruling said.
The Republican Party, which was set up on the basis of the Democratic Platform of the U.S.S.R. Communist Party in 1990, was last registered with the Justice Ministry in August 2002.
A representative of the Federal Registration Service, Galina Fokina, said the service was satisfied with the court ruling.
"The court has supported our position and agreed with our arguments that the number of party members does not meet the legal requirements," she said.
Fokina said the party had virtually stopped operating in 2004 and then suddenly resumed its activities in November-December 2005.
"Adopting a thousand new members to the party in a week sounds unrealistic and prompted us to check whether there were any law violations there," she said, adding that the probe had revealed that the party was short of the legal norm of 50,000 members.
The party, which strongly opposed the Kremlin's military campaign in Chechnya in the 1990s, said it would appeal against the ruling with the European Court of Human Rights in Strasbourg and the Constitutional Court of Russia, co-chairman Vladimir Ryzhkov said.
"We bluntly oppose the Supreme Court decision to close our party, and will appeal against the ruling," he said, adding that the court had failed to closely study the evidence provided by the party.
Representatives of the party brought five boxes of documents to the court to prove that the party had 58,166 members. "It means that our party fully meets the legal requirements," Ryzhkov said.
