We'll drink to lager milestone!
Rugby fans are expected to down in the region of 150,000 pints of Carling, the official lager supplier at the stadium.
One supporter will win a new Welsh rugby shirt, a "unique pitch side experience" plus a pair of tickets for the following three internationals if he buys the five millionth pint.
Roger Lewis, WRU chief executive, said: "It was an enjoyable day when we celebrated the three million pint milestone during the RBS Six Nations clash against Scotland at the Millennium Stadium in 2006 and we plan for another great occasion.
"Having a pint of beer is part of the international match experience for many ticket holders and we are very proud of our supporters and their ability to enjoy the social side of match day while continuing to behave responsibly and sensibly.
"This year the Autumn Series will showcase some of the best rugby in the world ahead of the Rugby World Cup and I'm sure the fans will not be disappointed."
Tickets are available for Wales v Australia and all Invesco Perpetual Autumn Series fixtures at www.wru.co.uk/tickets, via telephone 08442 777 888 and at Cardiff Arms Store, Westgate Street, Cardiff.