The men, who were convicted of common law assault by a military court, dragged the 17-year-old into their base in southern Kasai province after he was caught allegedly stealing buckets in January, the military said Monday.
Sixteen men were originally charged under anti-torture legislation over the incident but five were subsequently cleared of all charges, and the other 11 were not convicted of torture.
"The chief of the South African National Defence Force (SANDF), General Solly Shoke, welcomed the speedy trial and the successful conviction of those guilty of assault and tarnishing the good name of the SANDF peacekeepers in the DRC," said the statement.
The conflict-torn former Belgian colony is heading for long-delayed presidential and parliamentary elections on December 23. The government, which has a thorny relationship with the UN, has rejected all forms of international financial or logistical assistance for the election in a country nearly five times the size of France.
MONUSCO had suggested using its helicopters and planes to ferry imported voting machines to polling stations nationwide. But Kinshasa wants to see MONUSCO gone by 2020, ending a 20-year presence that has seen 16,000 troops deployed at an annual cost of more than a billion dollars.