A Sydney woman said her sister and sister's husband died in the country.
Queensland-born Amira Karroum, 22, went to school on the Gold Coast before moving to Granville in Sydney's west.
A Sydney activist corroborated the story - but the Department of Foreign Affairs has not yet been able to confirm the deaths.
"Consular officials are seeking to confirm the reported deaths of two Australians in Syria", the Department said in a statement.