Authorities seized 766 kilograms of the “highest purity” MDMA recorded in Queensland state, with a conservative street value of A$90 million ($61 million).
The bust involved coordination between Australian, New Zealand and British authorities.
“Organized crime syndicates are making significant profit at the expense of our Australian community but more importantly they are placing our young people’s health at risk,” Detective Superintendent Jon Wacker, of Queensland police, said in a statement.
Police said the MDMA was to be sold in pill and capsule form.
“We believe the drug would have been diluted with other agents and had the potential to make between six and 12 million capsules,” Wacker added.
Two British men aged 51 and 40 were arrested in Australia, along with a 26-year-old Queensland man, and face charges relating to drug possession and supply.
New Zealand police charged two more men from the UK, aged 60 and 49, after a separate linked bust of 200 kilograms of methamphetamine last week.
A 51-year-old woman was also arrested in Australia with connections to the syndicate.
Authorities estimate that Australians consume over 1.1 tons of MDMA each year.