Ha Huy Hoang, who has worked for a newspaper published by Vietnam's Foreign Ministry, was arrested in October 2014.
His lawyer Ha Huy Son said after a trial lasting a few hours in the capital Hanoi that Ha Huy Hoang was sentenced to six years in prison for spying for China.
He added Hoang "has rejected all charges against him".
According to an online report by the state-run Tuoi Tre newspaper, Hoang was accused of providing information to China about the internal issues in Vietnam since 2011 and had travelled to China at least six times to meet his handler in the city of Nanning in Guangxi province.
In recent years a number of Vietnamese officials, including police officers, have been arrested on espionage charges relating to China.
Vietnam is being very sensitive about the issues related to China.
Despite the deep-rooted resentment among its people and territorial squabbling over the South China Sea, the ruling Communist Party shares close but rocky ties with Beijing while China also lacks trust to Vietnam.
Some party members are currently supporting a withdrawal from Beijing’s influence on Vietnam which has recently improved relations with the United States.