We have entered a new Cold War, Hiroshima Day Committee convenor Denis Doherty said.
He said that earlier this year US President Barack Obama agreed to have $1 trillion spent on having nuclear weapons revitalised and made smaller, or in other words to make them more usable, and that Russia and China have repaid the favour by replenishing their weapons and making the delivery systems even better.
"It's time to get active again and call with us and many from around the world to ban nuclear weapons," he said.
The Sydney rally will start at 1pm in Hyde Park North, near the Archibald Fountain. A march to the Prime Minister's office at 1 Bligh Street will follow.