Mackenzie Lynne Dern[10] (born March 24, 1993) is an American and Brazilian[11] professional mixed martial artist and Brazilian Jiu-Jitsu practitioner currently competing in the women's Strawweight division of the Ultimate Fighting Championship (UFC).

[16] Dern was born in Arizona, the daughter of Megaton Dias, a highly decorated grappling competitor.

[17] As a child, she grew up travelling back and forth between Arizona and her father's native Brazil.

"[19] Dern began training by the age of three and practicing with her father and stepmother who is also a black belt, Luciana Tavares.

[20] She was then promoted to black belt by her father in December 2012, three months prior to her 20th birthday.

[22] Due to her six 1st place finishes at the Asian Open, Mackenzie is the only female Jiu-Jitsu competitor to have won Gold Medals, at Black Belt level, at each of the 5 principal/highest ranking IBJJF Gi Championships - the other events are the Worlds, the Euros, the Pan Ams and the Brazilian Nationals.

One of her biggest achievements in BJJ came when she managed to defeat Gabi Garcia despite a huge weight difference, becoming one of the few women to do so.

[23] Dern was scheduled to make her mixed martial arts debut against Kenia Rosas at Legacy FC 58.

[25] Dern was scheduled to fight Montana De La Rosa at Legacy FC 61.

The bout was initially scheduled to be contested at strawweight, but was later changed to catchweight, as Dern missed weight by 2.8 lbs.

Dern came in overweight for the second time in a row, missing weight by four pounds, and had to forfeit 20% of her purse.

[39] After a hiatus from maternity leave, Dern faced Amanda Ribas on October 12, 2019 at UFC on ESPN+ 19.

[41] Dern was expected to face Ariane Carnelossi on April 25, 2020 at UFC Fight Night 173.

[69] Dern faced Amanda Lemos, replacing Tatiana Suarez, on February 17, 2024, at UFC 298.

[74] Dern was scheduled to face Amanda Ribas in a rematch on December 14, 2024 at UFC on ESPN 63.

[75] However, the bout was moved for unknown reasons to January 11, 2025 in order to serve as the main event at UFC Fight Night 249.

[85] In February 2019, Dern announced that she had put her MMA career on hold due to pregnancy.

[86] According to Dern, she left Black House MMA after a reported incident concerning her original coach, Juan Gomez, where he got into a physical altercation with her husband over a disagreement about money.