Catholic blogger, Paulus Le Van Son and Protestant leader, Nguyen Van Oai were arrested without a warrant in 2011.
It has been reported that during the trial their legal assistance was restricted and they were pressured by the authorities to confess.
They were first arrested in August 2011, according to AsiaNews, during a series of raids against bloggers and human rights activists.
It is thought they had links with groups and religious organisations, environmental groups and anti-Chinese groups.
Both were given a four year sentence, and another four years on probation for attempting to "overthrow the legitimate government."
Speaking upon his release Van Oai said in recent months he had been subjected to repeated pressure to sign an act in which he pleaded guilty.
He said that he was told he would be released if he signed the confession, but this did not happen.
Reports from the country are also suggesting that Buddhist and Catholic leaders are being targeted.
Human Rights Watch (HRW) says there are between 150 and 200 bloggers and activists detained in Vietnamese prisons, guilty of having wanted to exercise basic human rights at present.
