A Hanoi court has sentenced dissident blogger Pham Viet Dao to 15 months in prison for "abusing democratic freedoms" after he wrote an online post criticising the government.
The court decision comes amid an increasing crackdown against dissenters in the communist autocracy.
"I don't think that my articles have had a bad impact on society," said Dao, who defended himself at the trial.
The judge said that Dao's acts had threatened trust in the Vietnamese leadership.
"The defendant's acts are dangerous to the society, causing anxiety among the public and reducing people's trust in the leadership of the [Communist] Party and the state."
The international NGO Human Rights Watch condemned the Vietnamese court's decision to jail Dao and called for his "immediate and unconditional" release.
"The Vietnamese authorities are shaming themselves before domestic and international public opinion by staging yet another political trial of a peaceful critic," said Brad Adams, Asia Director at the organisation.
International Federation of Human Rights (FIDH) President Karim Lahidji also criticised the decision.
"The imprisonment of Pham Viet Dao once again calls into question the Vietnamese government's stated commitment to respecting human rights," he said.
"In fact, Vietnam continues to behave as an authoritarian government that perceives every freedom, including freedom of opinion and expression, as a threat to its rule."
Last April, three prominent dissident bloggers were sentenced to jail in Vietnam for "anti-state propaganda" in cases highly criticised by human rights groups as well as US President Barack Obama.
The most notorious of the three to be arrested was Nguyen Hoang Hai aka Dieu Cay, who was sentenced to 12 years in prison.
Amnesty International has dubbed Cay a "prisoner of conscience" while Barack Obama said: "We must not forget (journalists) like blogger Dieu Cay, whose 2008 arrest coincided with a mass crackdown on citizen journalism in Vietnam."
Although the 1992 Vietnamese constitution recognises freedom of expression, the criminal code prohibits speech that criticises the government in any way.
At least 63 people were imprisoned for peaceful political expression in the Asian nation last year.