The leader of the ring, Vu Tien Manh, a senior official in the provincial Justice Department, received the longest term, of four and a half years in jail.
The defendants, who include three women, also face fines totalling 376 million dong ($27,000).
The judge in the trial said the group bought more than 170 new-born babies from unmarried Vietnamese women and desperate families in several northern provinces and then sold them to foreigners.
The sales went on for six years, until the ring was uncovered in 1998.
The judge said many of the children, each sold for between $1,000 and $1,500, were adopted by people from Belgium or France.
Adoptive parents were told that the children had been abandoned by their mothers.
Nine people were convicted in January on similar charges of child peddling in the southern province of An Giang, in the country’s first trial of this kind.
The French were the main adopters of Vietnamese children until 1999, when Paris stopped the programme because of concerns over Vietnamese adoption procedures.
In February, France and Vietnam signed a convention on co-operation in adoption matters which, when ratified, will allow legal adoptions to resume.