Wildlife rangers wanting to conduct a survey in the Virunga National Park left the area in May because of unrest that began in April with an army mutiny, the BBC reported.
"Extensive use of heavy machine guns, mortars and combat helicopters blocked all efforts to monitor and protect gorilla families that make their home in the surrounding forests," Park Director Emmanuel de Merode said.
Six families of mountain gorillas in the park have been missing since fighting broke out in the area between government and rebel forces, researchers said.
The army and the M23 rebel group have now agreed to allow the rangers to launch search operations for the gorillas in rebel-controlled territory, de Merode said.
"We are delighted and relieved that all sides in the conflict have recognized the need to protect [DR] Congo's only mountain gorillas," he said in a statement.
Forty-five rangers would work with local communities to try and track the gorillas, he said.
"After locating the gorilla families, the park's gorilla monitoring teams will individually identify each member of the family," he said.
Virunga is home to 480 of the world's 790 remaining mountain gorillas.