The party's incumbent leader Vladimir Kishenin said Friday he would appeal against the decision in an appeal court.
"I regret that the court has banned Russia's oldest party, which turned 109 earlier this year," Kishenin said in reference to the party's precursor which appeared in 1898 before the Bolsheviks seized power. "We will go on with our struggle."
He said that the Supreme Court's decision was "purely political."
With the true reasons behind the move still unclear, the Supreme Court upheld the suit filed by the Russian Registration Service, which said the party's activity was unlawful since it had failed to establish local offices with at least 500 members in the majority of Russian regions and refused either to dissolve or transform itself into a public organization by January 1, 2007.
Social Democratic party members said they had established 47 regional offices with over 500 members, while the law required representation in at least 45 regions.
Earlier, the Supreme Court upheld the Registration Service's suits to ban the Republican Party of Russia, the Russian Party of Peace and the Freedom and Rule of the People party, which have already been removed from the state register on account of low membership figures.
Latest reports said the Supreme Court would soon consider the Registration Service's suits to ban three other political parties, Galina Fokina, the Service's representative to the court, said Friday, although refused to name them.
