A pearl excavated from the remote Kimberley region of Western Australia is believed to be 2,000 years old.

The pearl was found in 2011, at a rock shelter in the Admiralty Gulf, 80 kilometres east of Kalumburu, by researchers from the University of Wollongong and the University of New England.

Associate Professor Kat Szabo said the pearl is "irreplaceable" because it is the only one ever recovered from an ancient site in Australia.

"A pearl has never been found in an archaeological site in Australia, and to have one that's 2,000 years old was really exciting for traditional owners, for locals and for everyone who was around," Dr Szabo said.

Dr Szabo said it had taken four years to analyse and date the pearl, because the team had to use non-invasive technology which would not damage it.

"That was a really big challenge actually to get the dates right."

She said the shell around the pearl, which was buried about 70 centimetres below the surface, was radiocarbon dated to about 2,000 years old.

Because the pearl is so round, the researchers had to prove it was not a man-made pearl which had simply fallen into that layer.

"Our challenge was to then establish it wasn't a cultured pearl, it was a genuinely old pearl that was 2,000 years old ... but we can't radiocarbon date because that requires taking a sample," he said.

A handful of cultured pearls were borrowed from Cygnet Bay Pearl Farm, north of Broome, for comparison.

"It didn't have the seed that cultured pearls have, and we could tell from the many, many layers which had been added on to create the pearl that it was over 10 years old," she said.

"So it had been growing in the animal for over 10 years.

"They're all the classic signatures of a natural pearl."

She said the pearl was in surprisingly good condition.

"It has a bit of a gold-rose lustre now but it's very hard to say, given it's been in the dirt for 2,000 years, how much of that is an original colouring or how of that has been sort of picked up from sediments around.

"But it's in very good condition given its age."

The pearl will go on display at the WA Maritime Museum later this month as part of the Lustre Exhibition.