State media reported the 21 men and 9 women were convicted of being part of four connected rings that smuggled nearly 2 tons of heroin from Laos into Vietnam and then on to China.
The 20-day trial in the northern province of Quang Ninh involved the largest number of defendants sentenced to death in a single trial in Vietnamese court history, said provincial court chief Ngo Duc.
It was not immediately possible to reach lawyers for the men.
The fairness of the Vietnam's criminal justice system has been questioned by human rights groups and foreign governments.
Vietnam has tough drug laws and possessing or trafficking 600 grams (21.16 ounces) of heroin can result in a death sentence.
There are currently nearly 700 people on the death row.
In 2011, the country switched from firing squads to lethal injection on humanitarian grounds. Since then it has only executed a handful of people because of the difficulty in acquiring the required drugs.
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