The activists, aged between 24 and 30, were arrested in June 2023. They are accused of "extremism" and spreading "false information" about the Russian army.
On Wednesday, all were sentenced to prison terms of between six and twelve years.
They belong to the youth movement Vesna, 'spring' in Russian, which was formed in 2022 in President Vladimir Putin's hometown of St. Petersburg.
The human rights organization Memorial, whose activities are banned in Russia, has previously classified the six activists as political prisoners.
Since Russia launched a full-scale invasion of Ukraine in 2022, the Russian government has significantly increased pressure on dissent. Many Russian opponents of the war have left the country.
