The round fifty cent coin was the highest-denomination and largest diameter coin of the Australian decimal coins, introduced in 1966. It has a nominal value of half an Australian dollar, equivalent to five shillings in the pre-decimal accounting system. Due to the large number minted in 1966, and the rising cost of silver, it was not made in any other year. It was replaced by a twelve-sided 50 cent coin in 1969, which retained its reverse of the Australian Coat of Arms.

The round fifty cent coin contained 80% silver and 20% copper but, because the value of silver quickly increased after the coins were issued, their bullion value became higher than their face value, so they were withdrawn from circulation. A total of 36.45 million coins were minted, with 14 million being put into circulation.

Round 50c coins are still legal tender, but they are rarely used as means of payment. As of 12 November 2023^[update], the bullion value of a round 50c coin was about AU$11.94^[1][2][3]