There is a new twist on Sydney's rat-race, this time involving a battle between real-life rodents.

A native rat is being re-introduced to Sydney to give the introduced species a run for its money.

On Thursday night scientists from the University of Sydney released 100 bogul rats in the Sydney Harbour National Park, and at a sanctuary at Manly.

Ecologist Grainne Cleary says once established it is hoped the bush rats will be able to compete with the black rat, which arrived in Sydney with European settlers.

"We've been killing black rats around the harbour so there's big gaps where there's no black rats," Dr Cleary said.

The black rat is one of many introduced species that have driven native animals out of Sydney since European settlement. ( CSIRO, file photo: AAP )

"We're putting the native bush rat in, the bush rat gets time to make it its home, find a place to live, find a place to eat.

"The black rats will then start invading, start to want to come in, there will be a bit of fight and we're pretty confident that the true Aussie battler, the bogul, will win out."

Dr Cleary says the bogul rat is also better news for Sydney's human residents.

She says unlike the black rat, bush rats do not generally get into homes and do not become a plague problem.