Conservationists say there are only about 17 to 22 animals left in the Garamba National Park in that country, formerly known as Zaire.
The World Conservation Union says this represents a loss of between 14 and 19 rhinos in 14 months since the last survey.
Heavily-armed poaching gangs are being blamed for the slaughter.
It is ironic that with peace returning to the region, the exploitation of large mammals has escalated, conservationists said.
"It is devastating and deeply frustrating to see fresh rhino and elephant carcasses throughout the southern sector," said Kes Hillman Smith of the park project.
"We have been fighting to save these rhinos and elephants and the Garamba Park for 23 years."
The northern white rhino was once widespread, with an estimated 2,250 animals across five African states in 1960.