The UN said in a statement that four others were wounded in the attack, one seriously, when their camp "was hit by an RPG 7 rocket and came under heavy fire, to which they responded forcefully".
The early morning attack has been blamed on Allied Democratic Forces (ADF) rebels opposed to President Yoweri Museveni's regime in Uganda, across the eastern border.
The incident took place at Mukungwe, a village south of Beni in the north of the province.
"The UN soldiers came under fire as they were occupying a position to seal off the zone south of Beni, said UN military spokesman Lieutenant-Colonel Frederic Medard.
He said the UN troops fired back, driving off the attackers.
Since Saturday, 3,500 DRC government troops and 600 UN soldiers have been engaged in a joint operation to get the Ugandan rebels out of the DRC, which they use for a rear base.
Uganda's government has for months been urging Kinshasa to move against the ADF/NALU (National Army for the Liberation of Uganda) forces.
The incident took place at Mukungwe, a village south of Beni in the north of the province, near where military action in DRC is underway, in a region plagued by militias and armed groups.
The statement described ADF/NALU as "a permanent source of insecurity to local people", estimating it had between 1,500 and 2,000 members, and said its members engaged in poaching and various kinds of illegal trafficking.
The UN estimates that so far 35 Ugandan rebels have been killed.
Three DRC soldiers have been killed and 16 injured.
Since the UN mission, called MONUC, was first set up in 1990, it has grown to become the world's biggest peacekeeping force, with 18,600 members deployed across a vast nation emerging from a devastating war.
Twenty UN soldiers have been killed on active service.