Sydney, Melbourne, Brisbane and Adelaide are for sale - not the cities themselves, just the .com.au websites.
Five internet sites - sydney.com.au, melbourne.com.au, brisbane.com.au, adelaide.com.au and auction.com.au - have been put up for sale as a package for a seven-figure sum.
Brisbane-based firm Domain Guardians is handling the sale of the websites, which are currently owned by an unidentified corporation.
Domain Guardians co-founder Mike Robertson says the parcel of Australian websites are the most important to come up for sale for some time because they mirror four of the nation's five largest capital cities.
'Domain names are seen as real estate on the internet,' Mr Robertson said on Wednesday.
'These sites are like ocean-front property.'
Mr Robertson said the websites could provide a local entity or international corporation the opportunity to become the dominant online player in Australia.
The city sites, for example www.sydney.com.au, might be suited to a media organisation which could put news on the site and cross-promote sales of cars and real estate.
'The options are limitless with what someone can do with these domains - that's why they are so valuable,' Mr Robertson said.
Mr Robertson said the websites had been largely undeveloped and had great potential to hold new content, get more traffic driven to the them from linked sites, and climb up search engine rankings.
Domain Guardians has begun pitching the domains to companies in the media, real estate, retail and travel industries.