Nguyen Huu Vinh, a former policeman, had connections to the ruling Communist Party elite. His assistant received three years. Both denied the charges.
They were detained in 2014. The "Ba Sam" blogs they were accused of posting attracted several million page views.
Earlier, police outside the court broke up protests seeking their release.
The one-party state is often criticised by rights groups for its intolerance of dissent. Vietnam's mainstream media are state-run and heavily regulated.
However, the internet has emerged as a forum for criticising the authorities.
Nguyen Huu Vinh's case differs from other dissident bloggers jailed in recent years because of his family background - his late father was a government minister and former ambassador to the Soviet Union.
Quynh Le of BBC Vietnamese says the blog, which began in 2007, was a mixture of news and commentary from a stable of distinguished contributors.
"I am completely innocent," Vinh told the court.
His assistant Minh Thuy Thuy said she did not know who had written the articles or posted them, the Associated Press reports.
The authorities said the two had lowered people's trust in the ruling party.
Presiding Judge Nguyen Van Pho said the articles "distort the lines and policies of the party and law of the state and vilify individuals".
A court in Hanoi has sentenced a well-known Vietnamese blogger to five years in jail after finding him guilty of publishing anti-state articles.