Rain delayed the toss but Flintoff decided to make first use of batting on a greenish-looking pitch under threatening skies.
More rain began falling soon after the toss was made and the covers were placed on the pitch.
Chris Read replaced Geraint Jones as wicketkeeper in England's only team change.
Jones was dropped after struggling with low scores in the series, culminating in a pair of ducks in the third Perth Test.
Australia named an unchanged team after bowling greats Shane Warne and Glenn McGrath announced that they will be playing their final two Tests in Melbourne and in Sydney next week.
Warne, 37, is poised to become the first bowler to capture 700 Test wickets in the fourth Test, his 144th. He needs just one wicket before his home town fans to achieve the target.
Australia regained the Ashes after winning the opening three Test matches in Brisbane, Adelaide and Perth.
The Australians are trying to emulate Warwick Armstrong team's 5-0 Ashes sweep 85 years ago.
The showpiece Test of Australian cricket is likely to create a new world record for a single day's attendance, although the weather could be an inhibiting factor.
All tickets have been sold for Boxing Day to surpass the 90,800 for the second day of the fifth Test against the West Indies at the Melbourne Cricket Ground (MCG) in February 1961.
Australia:Justin Langer, Matthew Hayden, Ricky Ponting (capt), Michael Hussey, Michael Clarke, Andrew Symonds, Adam Gilchrist (wk), Shane Warne, Brett Lee, Stuart Clark and Glenn McGrath. Mitchell Johnson (12th man).
England: Andrew Strauss, Alastair Cook, Ian Bell, Paul Collingwood, Kevin Pietersen, Andrew Flintoff (captain), Chris Read (wk), Sajid Mahmood, Matthew Hoggard, Steve Harmison and Monty Panesar. James Anderson (12th man).
Umpires: Aleem Dar (Pak), Rudi Koertzen (RSA)
Match Referee: Ranjan Madugalle (SL)