By Agence France-Presse
The cartel was convicted of smuggling drugs across the border between 2004 and 2015, according to a report on Thursday in An Ninh Thu Do newspaper, the official mouthpiece of Hanoi police.
Ringleader Dang Minh Chau was accused of leading the "dangerous criminal gang" but was spared a death sentence and handed life in prison because she has a young child.
Two other gang members were also handed life sentences.
"Dang Minh Chau will be sentenced to life in prison for illegal drug trafficking... because she has to raise her child who is under 36 months old," the police report said.
Two more people were jailed for between 12 and 18 months following the four-day trial in Hanoi, according to the state-run Vietnam News Agency.
Communist Vietnam has some of the toughest drug laws in the world.
Anyone convicted of possessing more than 600 grams (21 ounces) of heroin or more than 20 kilos of opium can face the death penalty.
Vietnam has vowed to tackle the illicit narcotics trade flowing into China, but crackdowns are hindered by the soaring demand for drugs, official corruption and a long porous border between the neighbours.
Death sentences are routinely handed out for drug convictions, and Vietnam is a leading executioner globally, according to Amnesty International.
A total of 429 prisoners were executed in the Southeast Asian country between August 2013 and June 2016, according to report published by Vietnam's Ministry of Public Security in January.
Since 2013, Vietnam has carried out death sentences by lethal injection, replacing executions by firing squads.