Williams also won the Australian Open in 2003, 2005 and 2007
Serena Williams swept aside Dinara Safina 6-0 6-3 to claim a fourth Australian Open crown and the 10th Grand Slam singles title of her career.
The American second seed, 27, stormed to the first set in just 22 minutes as the Russian crumbled under the pressure of her second Grand Slam final.
Safina, seeded three, did break at the start of the second set but Williams broke back and soon wrapped up victory.
The win in Melbourne also saw Williams become the new world number one.
She collected her second trophy in Melbourne this year after she and sister Venus took the women's doubles title on Friday.
I was just the ball boy on the court today
Williams went into the final with a 5-1 record and huge edge in Grand Slam experience over Safina, and it showed.
The Russian had disappointed in her first major final in Paris last year and it was a similar story this time as a relaxed and confident Williams powered to victory.
Three double faults in Safina's first service game gave a sign of things to come and some heavy forehands took Serena to a double break at 4-0.
The first set was over in 22 minutes when two more Safina errors handed over a third break of serve and a thrashing looked inevitable.
There was a brief glimpse of a competitive encounter when Safina broke at the start of the second set, hammering a backhand return past the American.
But, despite one very wayward volley, Williams broke back immediately and a couple more Safina double faults two games later made it 3-1.
The rest of the set went with serve, with no apparent danger of a Safina comeback and one air-shot providing an especially embarrassing moment for the Russian.
Williams clenched her fist as she fired an ace for 30-0 when serving for the match and two points later Safina sent a backhand wide to end the match after just 58 minutes.
"Not much to say as I didn't spend one hour on the court," Safina admitted afterwards.
"Serena Williams played just too good - I was just the ball boy on the court today."
Williams said: "Dinara will have a great future - she is hitting so hard I just had to go for broke against her."
A 10th major victory for Williams saw her climb to seventh in the all-time list of women's Grand Slam singles winners.
Australian Margaret Court tops the list with 24 titles ahead of Steffi Graf (22), Helen Moody (19), Chris Evert and Martina Navratilova (both 18).
Williams said she was thrilled to be included in their ranks, despite not seeing herself as an all-time great.
"I idolised Steffi Graf," she said. "When I played her I was like 'Oh My God, it's Steffi Graf'.
"Martina Navratilova was someone who was my role model, so when I think of these greats I don't really think of my name, I think of them.
"I think people are starting to think of me (in those terms), which is uber-cool, I can't even get my mind around that."