The very first Australian flag was unveiled in 1901 and no one has seen it since.
The Australian National Flag Association is searching for the first ever Aussie flag, which was flown at the Royal Exhibition Building in Melbourne 116 years ago.
It was then reportedly given to a museum, but no one knows which one.
"It's entirely possible that this precious piece of Australian history is in a community hall or museum, or possibly even in a private home, without anyone realising its significance," association president Allan Pidgeon said on Wednesday.
"(We're) asking all Australians to look closely at any old national flag they may have in their care, and to get in touch with us if they think it could be the very first Australian flag."
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A major clue for people checking their old flags - the large star on the first flag had just six points to represent the six states.
The seventh point was added to the flag from 1908 to represent the territories.
Based on reports at the time, Mr Pidgeon believes the first flag was about 11 metres by 5.5 metres in size.
Despite more than 100 years passing since the flag's last known sighting, Mr Pidgeon is optimistic.
"Just last year, the flag that had been draped across the grave of Breaker Morant in 1902 was found on a rubbish tip outside Tenterfield," he said.
"So there's every chance that the original Australian flag is also sitting unnoticed somewhere."
