Eleven Congolese army officers accused of rape, pillaging, destroying schools and abducting children were found guilty.
Among them were a commander who was jailed for life and his second in command, a major, who was also given life.
A military tribunal in the central African country's South Kivu province, where the rapes happened in September, sentenced them on Wednesday.
These verdicts show that efforts to end the culture of people going unpunished for rape are working and justice is possible, said the UN's Margot Wallström.
"This sends a strong signal to all perpetrators of acts of sexual violence that no military commander is beyond the law, including members of a national army," she said.
She praised the 21 women victims, who testified in court, stressing that it is crucial that the victims of and witnesses to f sexual violence are protected, as well as their families.
The UN agencies and human rights bodies have reported and condemned thousands of cases of rape notably in the eastern Kivu provinces of DRC, which are still prey to unrest. Rapes have been blamed on troops of the national army as well as the rebel movements and militias active in the region.
Last month, nine soldiers, including a lieutenant colonel, were jailed by the same court for raping about 60 women in January. They were handed prison sentences ranging between 10 and 20 years. This was the first time that a senior official and members of the Congolese army have been arrested, tried and sentenced for conflict-related sexual violence in the Democratic Republic of Congo, the United Nations said.
The United Nations has dubbed the war-torn country 'the rape capital of the world.' Every day, an average 14 women are sexually assaulted in Congo, according to the UN refugee agency. In the first three months of this year, 1, 244 women were sexually assaulted throughout DR Congo, according to UN data. And over the past 14 years, at least 200, 000 cases of sexual violence have been recorded.
Last year, the country reported 14,591 cases of sexual violence. At that figure includes thousands of children. Children are also abducted and forced to serve as soldiers in armed groups.