A quarter of a million people have taken to the streets in the city of Sydney.
Just like earlier protests in other countries, they're marching to show their anger at the thought of going to war with Iraq.
The Australian government strongly supports US president George Bush and UK prime minister Tony Blair.
They think Iraq should be attacked if it has weapons of mass destruction.
Biggest march for years
And tens of thousands have also been marching in other Australian cities - Adelaide, Brisbane and Darwin.
On Saturday, over a million people marched in London, UK.
And across the world, about ten million peace campaigners took to the streets.
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