Golden run but Kurt's waiting game continues
Wearing white and lime green Lycra, the tourists finished in 3:03.71s to end the four-day test event in the new stadium nicknamed the Birds Nest.
Silver went to Japan and bronze to China.
It follows gold at the Melbourne Commonwealth Games and silver at the 2004 Athens Olympics for the Australians.
"It was a good result for Australia out in the Olympic stadium," Mark Ormrod, who ran the third leg, said.
"We're starting to build a reputation, I think tonight, and it's good to show everybody, hey, we're still around, and come two months' time we're going to have a really strong team, so they better watch out."
Three of the four Australians - Daniel Batman, Ormrod and Mulcahy - are vying for the final spot in the relay squad of six for Beijing in August.
Ormrod, who won silver as part of the relay team at Athens, earlier won the individual 400m event in 46.45s.
Mulcahy finished seventh in 46.98s after winning his heat and semi-final.
Both his earlier runs saw the teenager post quicker times with a best of 46.54s in the heat.
However, neither Ormrod, Mulcahy nor Batman has run an Olympic A-qualifying time of 45.55s or a B-qualifying time of 45.95s this season.
While Ormrod is an Olympic silver medallist, Mulcahy gained big meet experience last year as part of the relay team that competed at the World Championships in Japan.
Clinton Hill, who anchored the relay in China on Sunday, said that the final place will likely be announced in July, after the selectors meet on June 23.
"We're not too sure who it's going to be and that's the frustrating thing," Hill said.
"We're all good mates and all three guys who are going for that spot are good buddies, it's just unfortunate that the systems put them in that position.
"But, at the end of the day, we're going to have the strongest team there and I think that's what any of the guys would want, is to have the strongest six guys there and the strongest four on the day."
John Steffensen, Dylan Grant, Joel Milburn, Hill and Sean Wroe are the runners already selected for the 4 x 400m squad.
Earlier, Batman grabbed a silver medal in the men's 200m final in 20.96 seconds, just behind Li Mingxuan of China (20.91 secs), although the Victorian wasn't too impressed with his performance.