| Fighter | Record | Last Bout |
|---|---|---|
| Juan Manuel Puig | 11-4-0 | 2014-11-22 |
| Juancamilo Ronderos | 4-2-0 | 2023-02-18 |
| Jules Bruchez | 1-2-0 | 2008-12-13 |
| Julian Sanchez | 0-1-0 | 1996-09-20 |
| Juliana Lima | 9-5-0 | 2018-01-27 |
| Julie Kedzie | 16-13-0 | 2013-12-06 |
| Julio Arce | 19-6-0 | 2024-03-30 |
| Julio Paulino | 23-5-0 | 2010-09-25 |
| Jumabieke Tuerxun | 19-4-1 | 2014-11-07 |
| Junie Browning | 5-6-0 | 2009-04-01 |
| Junior Albini | 14-6-0 | 2019-06-29 |
| Junior Assuncao | 16-6-0 | 2011-12-30 |
| Junior Dos Santos | 21-9-0 | 2020-12-12 |
| Jussier Formiga | 23-8-0 | 2020-06-06 |
| Justin Buchholz | 15-10-0 | 2010-02-06 |
| Justin Edwards | 9-5-0 | 2015-06-06 |
| Justin Eilers | 19-7-1 | 2006-02-04 |
| Justin Frazier | 10-3-0 | 2018-11-30 |
| Justin James | 13-7-0 | 2006-10-14 |
| Justin Jaynes | 16-8-0 | 2021-06-26 |
| Justin Jones | 9-2-0 | 2015-04-04 |
| Justin Lawrence | 10-4-0 | 2013-04-13 |
| Justin Ledet | 9-4-0 (1 NC) | 2020-10-31 |
| Justin Levens | 10-7-0 | 2006-06-28 |
| Justin Martin | 4-3-0 | 1997-02-07 |
| Justin McCully | 11-5-2 | 2009-08-29 |
| Justin Salas | 12-7-0 | 2016-03-05 |
| Justin Scoggins | 11-5-0 | 2018-07-14 |
| Justin Willis | 8-2-0 | 2019-03-23 |
| Justin Wren | 13-2-0 | 2009-12-05 |
| Justine Kish | 7-4-0 | 2021-04-17 |
| Jutaro Nakao | 25-19-4 | 2002-03-22 |
| Kailin Curran | 4-5-0 | 2017-11-25 |
| Kajan Johnson | 23-13-1 | 2018-09-15 |
| Kalib Starnes | 17-11-1 | 2008-04-19 |
| Kalindra Faria | 18-8-1 | 2018-08-25 |
| Kamal Shalorus | 9-5-2 | 2012-05-15 |
| Kamuela Kirk | 12-6-0 | 2023-07-08 |
| Kanako Murata | 12-3-0 | 2023-10-07 |
| Karine Gevorgyan | 3-3-0 | 2017-12-01 |
| Karl Roberson | 9-6-0 | 2022-07-09 |
| Karl Williams | 10-2-0 | 2024-08-10 |
| Karlos Vemola | 17-5-0 | 2013-06-08 |
| Karo Parisyan | 24-11-0 (1 NC) | 2010-11-20 |
| Katsuhisa Fujii | 9-18-1 | 1999-11-19 |
| Katsunori Kikuno | 24-8-2 | 2015-09-26 |
| Kay Hansen | 7-6-0 | 2022-04-09 |
| Kaynan Kruschewsky | 15-3-0 (1 NC) | 2024-07-20 |
| Kazuhiro Nakamura | 21-13-0 | 2008-05-24 |
| Kazuki Tokudome | 18-7-1 | 2014-09-20 |