A program to reintroduce eastern quolls to mainland Australia has achieved success with 15 babies found in the pouches of three adult females.

Twenty eastern quolls bred in a wildlife park in Tasmania were released into the Booderee National Park on the NSW South Coast in March.

At first there were serious concerns the repopulation program would not succeed as a number of the cute carnivorous marsupials became road kill, or fell prey to hungry foxes.

But pouch checks on the remaining females revealed that three were carrying five babies each.

Director of Rewilding Australia, Rob Brewster, was delighted with the find.

"To see those little babies was just fantastic," he said.

One of three female Eastern Quolls from Tasmania shown to be producing offspring in mainland breeding program near Jervis Bay. ( Supplied: Booderee National Park )

"We checked the pouch and it was a very exciting moment for the researchers to see what any reintroduction program wants to see after this amount of time," he said.

Mr Brewster said they were the first eastern quolls born in the wild on the Australian mainland in more than 50 years.

He said the group behind the program always knew that some of the quolls moved to the mainland would die and the challenge was to make it work.

The program was modified once they identified the risks.

"We relocated those quolls to a part of the park away from sealed roads and that has been really effective at reducing mortalities and allowing us to have this recent success," he said.

Eastern quolls can carry up to six young each, so to carry five is considered very successful.

The babies were small and pink resembling a bean.

In terms of their capacity to survive, Rob Brewster said the animals have to move long distances looking for food — so the high number of young helps to ensure some will make it through to the next breeding season.

The parents wear GPS collars with satellite tracking used to keep an eye on their progress.

Editor's note (10/7/18): The original version of this story incorrectly stated that it was the first time baby quolls had been born on the Australian mainland in 50 years, but has been amended to reflect that Rewilding Australia says they are the first eastern quolls born in the wild on the mainland in more than 50 years.