Belfort studied in Gracie Jiu-Jitsu with the Gracie family, namely Carlson Gracie. He received a black belt under Carlson.

At the age of 19, Vitor came to the US to compete. In his first sanctioned mixed martial arts match at an event called Superbrawl in Hawaii, his opponent was Jon Hess, whom the young Brazilian defeated in 12 seconds by KO.

Soon after, he moved on to compete in the UFC, where he was given the nickname The Phenom. He beat two fighters in his debut event in the UFC. Later he TKO-ed Tank Abbott in a non-tournament fight, knocking Tank down and using ground and pound tactics.

In 1997 Belfort fought against American Greco-Roman Wrestler Randy Couture. Belfort was upset by KO 8:16 into the match, his boxing skills negated by Couture's clinch and pound tactics.

After his defeat, he fought twice more in the UFC. His first fight was against a training partner of his: Joe Charles whom he defeated quickly via Armbar, without throwing a single punch.

A year later, Belfort faced rising Brazilian star Wanderlei Silva in the UFC. Catching Silva early with a left cross, he chased him across the ring with punches and pinned Silva against the fence, TKO-ing the Brazilian in 44 seconds.

Vitor then moved on to fight in Japan's PRIDE Fighting Championships. His first opponent was Kazushi Sakuraba in 1999. Vitor controlled the first minutes of the fight before suffering a hand injury. His striking skills now limited, Belfort resorted to falling to the ground repeatedly and attempted to get Sakuraba to get into his guard. Sakuraba however, stomped and kicked Belfort in his legs whilst he lay on his back. Belfort said after the fight "I didn't fight; I survived". Following the fight he stopped training with Carlson Gracie and started to train with Brazilian Top Team.

He fought four more times in PRIDE against Gilbert Yvel, Daijiro Matsui, Bobby Southworth and Heath Herring. For these matches Belfort utilised his stand up striking skills less and instead controlled the fights and won by ground and pound tactics. With the exception of his fight with Bobby Southworth (where he won via Rear Naked Choke in the first round), all his wins in PRIDE were by decision.

Returning to the UFC, Belfort was scheduled to fight Tito Ortiz in the main event of UFC's first Las Vegas show at UFC 33. However he acquired an injury prior to the event that required surgery. Belfort eventually returned and fought Chuck Liddell (loss via decision), then Marvin Eastman (win via TKO), opening a severe cut on Eastman's eyebrow with a knee strike.

His next major fight was on February 2, 2004 against Randy Couture, a rematch, after Vitor lost the first. Despite agonizing over his sister Priscila Belfort who disappeared on January 9, Vitor won the fight in 49 seconds when a seam from his glove cut Couture's eyelid, prompting a referee stoppage. Another rematch took place on August 21, 2004. Couture didn't consider that fight to be the rubber match, but rather a continuation of the second fight. Couture won via doctor stoppage after the third round, due to accumulated punishment and a cut which was opened by Couture.

(As of March 28, 2006, Priscila is presumed by Brazilian authorities to have been kidnapped and killed, by suspected drug dealers.[1])

His next fight was in the UFC against Tito Ortiz on February 5, 2005. Belfort broke Tito's nose with punches in a close first round and nearly stopped Ortiz in the second, but Vitor gassed out and Ortiz dominated him in the third. Belfort lost by controversial split decision.

Belfort entered PRIDE's Middleweight Grand Prix on April 23, 2005. He lost in the opening round to Dutch Golden Glory fighter Alistair Overeem via guillotine choke.

On December 3, 2005 Belfort fought Antony Rea and defeated him via KO at Cage Rage 14 in the second round.

On April 11, 2006 Vitor fought in his pro boxing debut against Josemario Neves. Belfort won by KO within the first minute after knocking his opponent down three times. Although he has fought in boxing, his main interest is to fight in MMA.

His next MMA fight was at the Strikeforce "Revenge" show on June 09, 2006: a rematch against Alistair Overeem. Belfort lost by unanimous decision.

On July 2, 2006, Vitor defeated the veteran Yoshiki Takahashi via KO in 36 seconds of the first round of PRIDE Critical Countdown Absolute.

At PRIDE 32: The Real Deal on October 21, 2006, Belfort lost a unanimous decision to PRIDE Welterweight Champion Dan Henderson (arguably most passive performance ever by Belfort). After the fight, Belfort tested positive for an illegal substance, 4-hydroxytestosterone. [2] In his defense, Belfort argued that he purchased an over the counter supplement known as 'Max Tribustak' at Max Muscle in La Habra, California, which contains 4-Hydroxytestosterone. Belfort also explained that he may have received 4-Hydroxytestosterone as the result of rehabilitative injections given to him by Brazilian endocrinologist Dr. Rodrigo M. Greco after his surgery to repair a torn meniscus in his knee in the summer of 2006. The NSAC eventually received a statement from Dr. Greco stating that he did give Belfort post surgical injections containing testosterone. While conceding that Belfort may have not known about the testosterone, the NSAC explained that even if Belfort was given injections by a medical practictioner who did not inform him that they contained anabolic steroids, it would still be a violation of the banned substances policy. On December 21, 2006 he was suspended for nine months from the date of the hearing and fined $10,000. [3].

Vitor Belfort defeated Ivan Serati by TKO at Cage Rage 21 in England on April 21.