Nguyen Dinh Ngoc is one of scores of activists and bloggers behind bars in Vietnam, which has one of the worst press freedom rankings in the world.
The 50-year-old, known by his pen name Nguyen Ngoc Gia, had his sentence reduced from four years to three, his lawyer Ha Huy Son told AFP.
"The decision was based on humanitarian reasons," Son said after the two-hour trial.
Several of his family members also died in the war and his father was a life-long member of the Communist Party.
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"The family rendered good services to the regime," Son said.
Ngoc was arrested in December 2014 in Ho Chi Minh City and in March this year was convicted of "propaganda against the communist state", which carries a maximum penalty of 20 years in prison.
The court today also upheld a three-year probation period for Ngoc.
The country ranks 175 out of 180 on Reporters Without Borders' latest press freedom index.
Today's ruling follows the failed appeal of anti-government blogger Nguyen Huu Vinh, known as Anh Ba Sam, whose five-year sentence for disseminating anti-government articles was upheld last month in Hanoi.