The unique pink argyle and white diamond ring, valued at $577,000, was nicked from a display counter at the centre in Alexandria, in Sydney's inner-east, between 12.30pm and 1.25pm on Saturday.
Each of the diamonds in the ring is laser inscribed with a serial number.
An attendant at the auction discovered the ring missing and contacted police.
Police are appealing for any witnesses to come forward.
Finding the ring might prove to be a challenge as about 100 people walked through the auction centre around the time it was stolen.
