Early career Jung made his professional debut in June 2007 and in December the same year, he won a Lightweight Tournament arranged by
Pancrase Korea. In 2008 he won both his fights for Japanese promotion
DEEP. He then entered the 2009
Sengoku Featherweight Grand Prix where he won his first-round fight but was eliminated from the tournament by the eventual winner
Masanori Kanehara. On August 16, 2008, he defeated
Michihiro Omigawa at
DEEP: Gladiator via unanimous decision. His next fight was against Fanjin Son at
DEEP: 39 Impact where he won via knockout in 17 seconds.
Sengoku Jung then entered the 2009 Sengoku Featherweight Grand-Prix and was matched up with Shintaro Ishiwatari in his first-round fight at
Sengoku 7. After dropping Ishiwatari once in stand-up striking, Jung hit Ishiwatari with a right hand forcing him to give up his back. From there Jung sunk in a
rear-naked choke submission forcing Ishiwatari to submit at 4:29 of the first round. In his second-round fight at
Sengoku 8 on May 2, 2009, he lost via unanimous decision to
Masanori Kanehara officially eliminating him from the tournament. The decision was considered questionable by the English commentators and many fans (especially given Sengoku's history of biased decisions against Korean fighters), who felt that Jung had done enough to deserve the decision. On June 7, 2009, it was announced Jung would face American Matt Jaggers at
Sengoku 9 in a reserve bout for the tournament with the winner stepping in as a replacement should some of the remaining fighters be unable to continue. Jung ended up winning the fight by
triangle choke submission at 1:25 of the second round, but was not required to step in as a replacement.
World Extreme Cagefighting Chan Sung Jung then signed with
World Extreme Cagefighting. He made his American and WEC debut against
Leonard Garcia (who replaced injured opponent
Cub Swanson) on April 24, 2010 at
WEC 48 Jung lost the fight via split decision. Many MMA publications and fans (including many in the
Sacramento home crowd) opposed the decision, which has led again to questions about the accuracy of the fight judging. However, the bout was awarded the
Fight of the Night honors, this was later declared the
Fight of the Year by the
Wrestling Observer Newsletter. Jung next faced
George Roop on September 30, 2010, at
WEC 51. He lost the fight via knockout due to a head kick in the second round.
Ultimate Fighting Championship Jung was expected to face
Rani Yahya on January 22, 2011, at
UFC Fight Night 23. However, Jung was forced from the card with an injury. A rematch with Garcia was scheduled for March 26, 2011, at
UFC Fight Night 24, after Jung stepped in to replace an injured
Nam Phan. Jung was able to avenge the original loss after submitting Garcia with a
twister in the final second of the second round. This was the first time in the history of the UFC that a twister submission finished an opponent and the win earned Jung his first
Submission of the Night honors. This was later awarded for the
Submission of the Year by the World MMA Awards. In his post-fight interview, Jung stated he learned the move by watching
Eddie Bravo videos on
YouTube. Jung's victory over Mark Hominick earned him a $75,000
Knockout of the Night bonus. The victory also earned Jung much praise in his native South Korea, appearing on news broadcasts on the country's major national television channels (such as
KBS). Jung faced
Dustin Poirier on May 15, 2012, at
UFC on Fuel TV: Korean Zombie vs. Poirier. Jung defeated Poirier via submission in the fourth round. The performance earned Jung
Submission of the Night and both participants
Fight of the Night honors. The bout was honored as Fight of the Year and Submission of the Year by several publications at the conclusion of 2012. This fight was the first time that Jung walked out to the song
Zombie by
The Cranberries. He would use this for every fight thereafter. Jung was expected to face
Ricardo Lamas on July 6, 2013, at
UFC 162. However, on June 14, it was announced that Jung had been pulled from the Lamas bout and would replace an injured
Anthony Pettis to face
José Aldo for the
UFC Featherweight Championship on August 3, 2013, at
UFC 163. Aldo defeated Jung via fourth-round TKO, finishing Jung with a flurry of strikes after Jung suffered a dislocated shoulder while throwing an overhand right. Jung was expected to face
Akira Corassani on October 4, 2014, at
UFC Fight Night 53. However, Jung pulled out of the bout citing another injury and was replaced by
Max Holloway. Jung announced in mid-October 2014 his intention to begin his stint for
mandatory military service in his home country of South Korea. While Jung did not comment about the future upon his completion, his manager indicated that he would return to mixed martial arts at the end of the two years. In mid 2016, Jung attended
Rener Gracie's inaugural Korean Super Seminar in Seoul. Jung faced
Dennis Bermudez on February 4, 2017, at
UFC Fight Night 104. He won the fight by knockout in the first round. The win also won Jung his first
Performance of the Night bonus award. Jung was expected to face
Ricardo Lamas on July 29, 2017, at
UFC 214. However, Jung pulled out of the fight in early June citing a knee injury. He was replaced by
Jason Knight. Jung was expected to face
Frankie Edgar on November 10, 2018 at
UFC Fight Night 139. However, it was reported on October 26, 2018 that Edgar was pulled from the bout due to injury and he was replaced by
Yair Rodríguez. He lost the fight via knockout in the final second of the fifth round. Both participants received
Fight of the Night honors. Jung faced
Renato Moicano on June 22, 2019 at
UFC Fight Night 154. He won the fight via technical knockout in 58 seconds of the first round. This fight earned him the
Performance of the Night award. Jung was scheduled to face
Brian Ortega on December 21, 2019 at
UFC Fight Night 165. However, Ortega pulled out of the fight in early December citing a knee injury and he was replaced by
Frankie Edgar. Jung won the fight via TKO in the first round. The win also earned Jung a
Performance of the Night bonus award. The bout against
Brian Ortega was rescheduled on October 18, 2020 at
UFC Fight Night 180. He lost the fight via unanimous decision. Jung faced
Dan Ige on June 19, 2021 at
UFC on ESPN 25. He won the fight via unanimous decision. Following the fight, Jung was promoted to the rank of black belt in
Brazilian Jiu Jitsu. Jung challenged for the
UFC Featherweight Championship for a second time against
Alexander Volkanovski at
UFC 273 on April 9, 2022. After being out struck and knocked down multiple times throughout the fight, Jung lost the fight via TKO early in round four. For the last time in his MMA career, Jung faced
Max Holloway on August 26, 2023 at
UFC Fight Night 225. Jung would go on to lose to Holloway via third round KO and subsequently announced his retirement after the fight. This bout earned the fighters a
Fight of the Night award. ==Championships and accomplishments==