The deaths of another two Tasmanian devils bred in captivity in a bid to ensure the species' survival has brought the number killed on the state's roads to four.

The release of 20 devils last month was hailed as a turning point in the fight against a fatal facial cancer that has threatened to wipe the devils out.

Previously, healthy animals had only been released into the wild on Tasmania's Maria Island which did not have an existing population.

Last week two of the devils released into the Narawntapu National Park (NNP) were found killed by the roadside.

On Saturday the Department of Primary Industries, Parks, Water and Environment (DPIPWE) confirmed another two had been found killed.

Sorry, this video has expired Devil takes first steps into the wild ( Troy Melville )

Save the Tasmanian Devil Program (STDP) team leader Samantha Fox pleaded with motorists to take more care.

"Sadly, the two deaths this morning bring to four the number of devils road-killed from the NNP release," Dr Fox said.

"Next to devil facial tumour disease, road-kill is the greatest threat that devils face.

"We urge all motorists to consider this when driving at night. Driving slowly is not only good road safety sense but is also good for Tasmania's wildlife."

The dead devils will undergo post-mortem examination on Monday to confirm the cause of death but parks officers said the animal's injuries appeared to be consistent with being struck with a vehicle.