Pham Minh Hoang, 56, was convicted of trying to overthrow the government by posting 33 articles against Vietnam's one-party communist regime, as well as of holding membership and recruiting others to join the banned Viet Tan group. It was the second high-profile dissident trial in just over a week.
The U.S.-based Viet Tan group says it is a nonviolent promoter of democracy, but Hanoi considers it a terror organization -- a claim U.S. officials have said they found no evidence to support.
Hoang told the court during the half-day trial in Ho Chi Minh City that he joined Viet Tan in France where it is not banned, but said he did not do anything to oppose the government, according to defense lawyer Tran Vu Hai.
Hoang, who was teaching math at a Ho Chi Minh City university at the time of his arrest, said he had returned to Vietnam in 2000 to contribute to the country and take care of his ailing parents, Hai said.
The court convicted him, however, on charges that also included attending a Viet Tan-organized course in Malaysia and helping to recruit new Vietnamese members, Hai said.
The communist government does not tolerate dissent, and rights groups allege it uses vague national security laws to imprison anyone who challenges its rule. Hanoi maintains only lawbreakers are jailed, but there has been a wave of crackdowns since the country's new government took over last month.
Last week, an appeals court in Hanoi upheld the seven-year prison sentence for the dissident son of one of Vietnam's founding revolutionaries, despite arguments that his support for a multiparty system did not mean he was against the Communist Party.
The ruling against Cu Huy Ha Vu drew immediate criticism from activists, the U.S. government and the European Union.
Wednesday's Communist Party newspaper Nhan Dan quoted Foreign Ministry spokeswoman Nguyen Phuong Nga as saying Hanoi rejected what it called "statements that interfere with its internal affairs."
The U.S. two weeks ago also called for the immediate release of one of Vietnam's best-known pro-democracy activists, a Roman Catholic priest suffering from a brain tumor. The Rev. Thadeus Nguyen Van Ly, 65, was sent back to prison after being granted more than a year of medical leave.