They were among 220 girls abducted from their school dormitories in Chibok by the terror group.
The girls, who are mostly Christians, were forced to marry their captors and give birth to their children.
A Nigerian military official said the freed girls were found near the town of Banki in Borno state, near Cameroon, but there are 113 girls still missing.
On Friday, the United States and Britain issued warnings that the group was actively planning to kidnap foreigners in in Borno state.
The 2014 mass kidnapping triggered the worldwide #Bringbackourgirls campaign.
It has put tremendous pressure on Nigeria's government to counter the extremists, who have roamed large parts of the north and into neighbouring countries.
Enoch Mark, a pastor whose two daughters were kidnapped by the terror group said: "This is good news to us. We have been waiting for this day.
"We hope the remaining girls will soon be released."
Buky Shonibare, who founded #Bringbackourgirls, said she's thankful for the release but said the girls went through extremely traumatic events.
She said: "This is a very, very exciting news for us that we have over 80 of our girls coming back again.
"Their life in captivity has been one that depicts suffering, it depicts the fact that they have been starved, abused, and as we have seen before some of those girls have come back with children, and some of them have also come back with news of how they have been sexually abused."
According to the Nigerian government, the latest negotiations were mediated by the Swiss government and the International Committee of the Red Cross.
Nigerian President, Muhammadu Buhari, said in a statement he will receive the released schoolgirls in capital Abuja.
