UFC 63: Hughes vs. Penn was a mixed martial arts event held by the Ultimate Fighting Championship on September 23, 2006. The event took place at the Arrowhead Pond in Anaheim, California and was broadcast live on pay-per-view in the United States and Canada.
The event, originally subtitled "Hughes vs. St. Pierre," was scheduled to feature a UFC Welterweight Title match between champion Matt Hughes and Georges St. Pierre and was officially announced during the July 17, 2006 edition of the The Hot List on ESPNEWS.  The fight was first announced, without a date, at a press conference in Toronto, Canada on April 7, 2006, and the matchup was alluded to—but not officially announced—during the PPV broadcast of UFC 58.
However, a groin injury—which was reported early in August—forced St. Pierre off the card. At first, St. Pierre sought a physiotherapist, hoping the injury would heal on its own during training. However, it was later announced that St. Pierre would indeed withdraw from his long-awaited title shot. Taking his place will be former UFC Welterweight Champion, B. J. Penn, who defeated Hughes in a championship fight in 2004, and was beaten by St. Pierre earlier this year.
Lightweight bout: Tyson Griffin vs. David Lee
Tyson Griffin defeats David Lee by submission (rear naked choke) at 1:50 of round one. The fight, although preliminary, was aired on the broadcast.
Lightweight bout: Jorge Gurgel vs. Danny Abaddi
Gurgel defeats Abbadi (from the The Ultimate Fighter 3) by unanimous decision after three rounds. Judges scored the bout 29-28 for Gurgel. Initially, it appeared one judge scored 29-28 in favor of Abbadi, making the bout a split decision victory for Gurgel. It was later reported that one of the scorecards was incorrectly labeled, and that Gurgel had actually earned the unanimous decision, despite the initial announcement. This preliminary bout was not aired on the broadcast.
Heavyweight bout: Mario Neto vs. Eddie Sanchez
Sanchez defeats Neto by knockout due to a punch at :17 of round two. Sanchez accepted the fight on short notice, replacing Gabriel Gonzaga. The fight, although preliminary, was aired on the broadcast.
Lightweight bout: Roger Huerta vs. Jason Dent
Huerta defeats Dent by unanimous decision after three rounds. All three judges scored the bout 30-27 for Huerta. Dent came as a late replacement for Jason Reinhardt, who had pulled out of the card due to lingering medical concerns with his neck.  This preliminary bout was not aired on the broadcast.
Lightweight bout: Jens Pulver vs. Joe Lauzon
Lauzon upsets Pulver by technical knockout due to strikes at :48 of round one. Pulver, the only UFC Lightweight Champion ever, was a 7 to 1 favorite in this match.
Light Heavyweight bout: Rashad Evans vs. Jason Lambert
Evans defeats Lambert by knockout due to punches from the mounted position at 2:22 of round two.
Lightweight bout: Melvin Guillard vs. Gabe Ruediger
Guillard defeats Ruediger by knockout due to a body punch at 1:01 of round two. Guillard had stifled Ruediger's offense in the opening half of the first round before succumbing to a takedown. At that point, Ruediger capitalized on the position, securing the back mount position and working for a rear naked choke before the round ended. Guillard continued to stifle Ruediger's takedowns in the second round before achieving the knockout from a punch to Ruediger's sternum – a finish seldom seen in mixed martial arts.
Middleweight bout: Mike Swick vs. David Loiseau
Swick defeats Loiseau by unanimous decision. All three judges scored the bout 29-28 for Swick.
Welterweight Championship bout: Champion Matt Hughes vs. B.J. Penn
In the main event of the evening, Matt Hughes defends his championship and defeats "The Prodigy" B.J. Penn by technical knockout (referee stoppage) due to strikes at 3:53 of round three. Hughes, who self-admittedly said he lost the first two rounds, and who nearly succumbed to a triangle choke/armbar combination from Penn at the end of round two, was able in the third round to gain side control of Penn and trap his two arms beneath him (one under his legs, the other under his left arm) while delivering a series of blows to the head.
In an interview on his own website after the fight, Penn claimed that he separated his ribs at the end of the second round in an attempt to sweep to Hughes' back. While the initial doctors report did not show any injuries, a later examination found that Penn did fracture his ribs at a costochondral junction and strained the adjacent intercostal and oblique musculatures.
The fight was given heightened interest, as Penn was the last person to defeat Hughes in mixed martial arts.
The disclosed fighter payroll for UFC 63 was $332,000. Individual payouts are listed below, note that numbers only include figures the UFC disclosed to the state athletic commission, and does not include PPV buyrate bonuses, sponsorship fees, or any other bonuses.
Title Match & Main Event Fighters
- Matt Hughes: $130,000 (defeated BJ Penn)
- BJ Penn: $50,000 (lost to Matt Hughes)
Main Card Fighters
- Jens Pulver: $30,000 (lost to Joe Lauzon)
- Rashad Evans: $24,000 (defeated Jason Lambert)
- Mike Swick: $14,000 (defeated David Loiseau)
- Melvin Guillard: $10,000 (defeated Gabe Ruediger)
- Jason Lambert: $9,000 (lost to Rashad Evans)
- David Loiseau: $9,000 (lost to Mike Swick)
- Joe Lauzon: $6,000 (defeated Jens Pulver)
- Gabe Ruediger: $3,000 (lost to Melvin Guillard)
Preliminary Match Fighters
- Tyson Griffin: $14,000 (defeated David Lee)
- Jorge Gurgel: $10,000 (defeated Danny Abaddi)
- Roger Huerta: $6,000 (defeated Jason Dent)
- Danny Abaddi: $5,000 (lost to Jorge Gurgel)
- Eddie Sanchez: $4,000 (defeated Mario Neto)
- Jason Dent: $3,000 (lost to Roger Huerta)
- Mario Neto: $3,000 (lost to Eddie Sanchez)
- David Lee: $2,000 (lost to Tyson Griffin)