Russia's Supreme Court has ruled that Jehovah's Witnesses was an "extremist" organisation and must hand over all its property to the state, according to reports from Russian news agencies.
Interfax news agency quoted Sergei Cherepanov, a Jehovah's Witnesses representative, as saying that the group will appeal the decision in the European Court of Human Rights.
"We will do everything possible," he said.
Russian authorities have put several of the group's publications on a list of banned extremist literature, while prosecutors have long cast it as an organisation that destroys families, fosters hatred and threatens lives.
The group, a United States-based nontrinitarian Christian denomination known for its door-to-door preaching and rejection of military service and blood transfusions, says this description is false.
The religious organisation has expanded around the world and has about eight million active followers.
It has faced court proceedings in several countries, including Ireland, mostly over its pacifism and rejection of blood transfusions, but has Russia has been most outspoken in portraying it as an extremist cult.
Its Russian branch, based near St Petersburg, has regularly rejected this allegation.
It has said a ban would directly affect around 400 of its groups and have an impact on all of its 2,277 religious groups in Russia, where it says it has 175,000 followers.