Among those sentenced were the heads of two welfare centers who helped persuade unwed pregnant mothers to give up their babies in exchange for free food and shelter.
The six were convicted of "abuse of power and authority," said Chief judge Dang Viet Hung of Nam Dinh provincial court.
Ten others were given suspended sentences in the scam, which involved filing false paperwork for 323 babies.
Many of the babies are believed to have been adopted by parents in the United States and Italy.
The adoption ring offered young unwed mothers free food and shelter at two welfare centers in exchange for giving up their babies, Hung said. They also solicited babies from desperately poor families, Hung said.
The ring then filed false paperwork claiming that the babies had been abandoned, which made them eligible for adoption.
State media have reported that the defendants had suggested and received $500 to $550 from adoptive parents for each adoption.
Vietnam and the United States, one of the Southeast Asian country's largest recipients of children for adoption, have yet to renew their bilateral adoption agreement that expired in September.
The U.S. Embassy said in a report in April last year that Vietnam had failed to police its adoption system, allowing corruption, fraud and baby-selling to flourish.
The report described brokers scouring villages for babies, hospitals selling the infants of mothers who cannot pay their bills, and a grandmother giving away her grandchild without telling the child's mother.