The harsh punishments are part of an escalating crackdown on dissent by the communist regime, which has triggered growing international concern.
The defendants were convicted of trying to overthrow the government -- a charge which rights groups say is routinely laid against peaceful activists.
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The group's 65-year-old "ringleader" Phan Van Thu received a life sentence, while the other 21 defendants were given between 10 and 17 years followed by up to five years' house arrest, lawyer Nguyen Huong Que told AFP.
"Most of the defendants admitted their crime of aiming to overthrow the people's administration," said the lawyer, who was appointed by the court to defend the accused at the week-long trial in the central province of Phu Yen.
"The sentences are adequate for their crimes," he added.
"We are profoundly shocked by the length of the sentences," said Phil Robertson, Asia deputy director at New York-based Human Rights Watch (HRW). "It seems to be another hammer blow against basic human rights in Vietnam."
The 22 were accused of running a "reactionary" group disguised as an eco-tourism operator, which produced documents "slandering" the regime and distorting its guidelines and policies, according to state media.
Dozens of activists have been jailed since Vietnam -- a one-party state that forbids political debate -- began a new crackdown on free expression in late 2009.
According to HRW, Vietnam jailed at least 33 activists in 2012 based on vaguely defined articles in its penal code that criminalise the exercise of civil and political rights.
"Authorities arbitrarily arrest activists, hold them incommunicado for long periods without access to legal counsel or family visits, subject them to torture, and prosecute them in politically pliant courts that mete out long prison sentences," the group said in its recent annual report.
In another mass trial last month, Vietnam jailed 13 activists -- including Catholics, bloggers and students -- a move criticised by the United States as part of a "disturbing" trend in the authoritarian state.
Last week Hanoi deported an American pro-democracy activist of Vietnamese origin after detaining him for nine months on charges of attempting to overthrow the state.
In December Prime Minister Nguyen Tan Dung ordered a new crackdown on online dissent, telling authorities to fight against anyone using the Internet to "defame and spread propaganda against the party and state".
Vietnam bans private media and all newspapers and television channels are state-run. Vietnamese lawyers, bloggers and activists are regularly subject to arbitrary arrest and detention, according to rights groups.
