| Emily Kagan (inactive) | | 0-2-0 | United States | Dec 10, 2015 |
| Sirwan Kakai (inactive) | Zohan | 1-1-0 | Sweden | Aug 8, 2015 |
| Saidyokub Kakhramonov (inactive) | | 2-1-0 | Uzbekistan | Dec 17, 2022 |
| Geza Kalman (inactive) | | 1-1-0 | Unknown | Jul 12, 1996 |
| Martin Kampmann (inactive) | The Hitman | 11-6-0 | Denmark | Aug 28, 2013 |
| Bharat Kandare (inactive) | Daring | 0-1-0 | India | Nov 25, 2017 |
| Masanori Kanehara (inactive) | | 1-2-0 | Japan | Jan 2, 2016 |
| Denis Kang (inactive) | | 1-2-0 | France | Nov 14, 2009 |
| Kyung Ho Kang (inactive) | Mr. Perfect | 8-5-0 (1 NC) | South Korea | Jun 22, 2024 |
| Zhu Kangjie | | 0-1-0 | China | May 30, 2026 |
| Manel Kape | StarBoy | 8-3-0 | Angola | Jun 20, 2026 |
| David Kaplan (inactive) | Diamond | 0-2-0 | United States | May 23, 2009 |
| Kai Kara-France | Don't Blink | 8-5-0 | New Zealand | Jun 28, 2025 |
| Alex Karalexis (inactive) | The Assassin | 1-2-0 | United States | Jan 16, 2006 |
| Ernesta Kareckaite | Heavy-Handed | 1-2-0 | Lithuania | Feb 28, 2026 |
| Impa Kasanganay (inactive) | Tshilobo | 2-2-0 | United States | Sep 18, 2021 |
| Nadia Kassem (inactive) | | 1-2-0 | Australia | Oct 5, 2019 |
| Yusuke Kasuya (inactive) | | 0-2-0 | Japan | Nov 26, 2016 |
| Brad Katona (inactive) | Superman | 4-5-0 | Canada | May 10, 2025 |
| Calvin Kattar | | 7-8-0 | United States | Jul 12, 2025 |
| Sarah Kaufman (inactive) | | 1-2-0 (1 NC) | Canada | Dec 19, 2015 |
| Lone'er Kavanagh | | 3-2-0 | United Kingdom | Jul 11, 2026 |
| Tatsuya Kawajiri (inactive) | Crusher | 3-3-0 | Japan | Aug 6, 2016 |
| Toshiomi Kazama | | 1-3-0 | Japan | Aug 9, 2025 |
| Julie Kedzie (inactive) | | 0-2-0 | United States | Dec 6, 2013 |
| Losene Keita | Black Panther | 1-1-0 | Guinea | Sep 5, 2026 |
| CJ Keith (inactive) | | 0-2-0 | United States | Jan 19, 2013 |
| Chris Kelades (inactive) | The Greek Assassin | 2-2-0 | Canada | Apr 23, 2016 |
| Brian Kelleher (inactive) | Boom | 8-9-0 | United States | Jul 20, 2024 |
| Tony Kelley (inactive) | Primetime | 2-2-0 | United States | Jun 18, 2022 |
| Daniel Kelly (inactive) | | 6-4-0 | Australia | May 27, 2018 |
| Paul Kelly (inactive) | | 5-4-0 | United Kingdom | Feb 5, 2011 |
| Song Kenan | The Assassin | 6-5-0 | China | Nov 23, 2024 |
| Jeremy Kennedy (inactive) | JBC | 3-1-0 | Canada | Feb 10, 2018 |
| Steve Kennedy (inactive) | The Steamrolla | 0-2-0 | United Kingdom | Nov 14, 2015 |
| Tim Kennedy (inactive) | | 3-2-0 | United States | Dec 10, 2016 |
| Casey Kenney | | 5-3-0 | United States | Aug 7, 2021 |
| Mark Kerr (inactive) | The Smashing Machine | 4-0-0 | United States | Oct 17, 1997 |
| Rustam Khabilov (inactive) | Tiger | 10-3-0 | Russia | Nov 9, 2019 |
| Sergey Khandozhko (inactive) | Honda | 2-1-0 | Russia | Apr 23, 2022 |
| Aliaskhab Khizriev | Black Wolf | 1-0-0 (1 NC) | Russia | Feb 3, 2024 |
| Pannie Kianzad (inactive) | Banzai | 5-6-0 | Iran | Aug 10, 2024 |
| Katsunori Kikuno (inactive) | | 2-3-0 | Japan | Sep 26, 2015 |
| Sanae Kikuta (inactive) | | 1-0-0 | Japan | Apr 14, 2000 |
| Jacob Kilburn (inactive) | The Killer | 0-2-0 | United States | Jan 16, 2021 |
| Dong Hyun Kim (inactive) | Stun Gun | 13-4-0 (1 NC) | South Korea | Jun 17, 2017 |
| Ji Yeon Kim (inactive) | Firefist | 3-7-0 | South Korea | May 13, 2023 |
| Sangwook Kim | Frogman | 0-1-0 | South Korea | Jan 31, 2026 |
| Jeremy Kimball (inactive) | | 1-3-0 | United States | Jul 22, 2018 |
| Rob Kimmons (inactive) | The Rosedale Reaper | 3-4-0 | United States | Mar 3, 2011 |
| Dustin Kimura (inactive) | The Diamond | 2-3-0 | United States | Dec 13, 2014 |
| Mike King (inactive) | | 0-1-0 | United States | Jul 19, 2014 |
| Kyle Kingsbury (inactive) | Kingsbu | 4-5-0 | United States | Jul 26, 2014 |
| Yusaku Kinoshita (inactive) | | 0-2-0 | Japan | Aug 26, 2023 |
| Kamuela Kirk | The Jawaiian | 1-2-0 | United States | Jul 8, 2023 |
| Justine Kish (inactive) | | 3-4-0 | Russia | Apr 17, 2021 |
| Koji Kitao (inactive) | | 0-1-0 | Japan | May 17, 1996 |
| Ludovit Klein | Mr. Highlight | 8-4-1 | Slovakia | Aug 1, 2026 |
| Nick Klein | Blue Collar | 0-2-0 | United States | Aug 2, 2025 |
| Fatima Kline | The Archangel | 4-1-0 | United States | Jul 18, 2026 |
| Drakkar Klose | | 10-4-0 | United States | Sep 12, 2026 |
| Jason Knight (inactive) | The Kid | 4-5-0 | United States | Nov 3, 2018 |
| William Knight (inactive) | Knightmare | 3-4-0 | United States | Feb 18, 2023 |
| Josefine Knutsson (inactive) | Thunder | 2-1-0 | Sweden | Dec 14, 2024 |
| Seokhyeon Ko | Technical | 2-1-0 | South Korea | Jul 18, 2026 |
| Erik Koch (inactive) | Phoenix | 5-5-0 | United States | Jul 27, 2019 |
| Brad Kohler (inactive) | | 1-1-0 | United States | Sep 24, 1999 |
| Tsuyoshi Kohsaka (inactive) | TK | 3-3-0 | Unknown | May 10, 2002 |
| John Kolosci (inactive) | | 0-1-0 | United States | Dec 8, 2007 |
| Syuri Kondo (inactive) | | 1-3-0 | Japan | Jun 22, 2019 |
| Yuki Kondo (inactive) | | 1-2-0 | Japan | Jun 29, 2001 |
| Mantas Kondratavicius | | 1-0-0 | Lithuania | Mar 21, 2026 |
| Cheick Kongo (inactive) | | 11-6-1 | France | Apr 27, 2013 |
| Roman Kopylov | | 8-5-0 | Russia | Oct 3, 2026 |
| Bruno Korea (inactive) | | 0-1-0 | Brazil | Nov 7, 2015 |
| Josh Koscheck (inactive) | | 15-10-0 | United States | Mar 21, 2015 |
| Steven Koslow | Obi Won Shinobi The Pillow | 0-1-0 | United States | Dec 10, 2022 |
| Naoyuki Kotani (inactive) | | 0-5-0 | Japan | Sep 26, 2015 |
| Karolina Kowalkiewicz | | 9-10-0 | Poland | Oct 11, 2025 |
| Derrick Krantz (inactive) | D-Rock | 0-2-0 | United States | Aug 31, 2019 |
| James Krause | The | 9-4-0 | United States | Oct 17, 2020 |
| Pascal Krauss (inactive) | Panzer | 2-2-0 | Germany | Aug 31, 2013 |
| Kaynan Kruschewsky (inactive) | Bahia | 0-2-0 | Brazil | Jul 20, 2024 |
| Nikita Krylov | The Miner | 12-10-0 | Ukraine | Jul 11, 2026 |
| Michael Kuiper (inactive) | | 1-3-0 | Netherlands | Oct 26, 2013 |
| Anton Kuivanen (inactive) | | 1-2-0 | United States | Feb 23, 2013 |
| Aleksei Kunchenko (inactive) | | 2-2-0 | Russia | Mar 14, 2020 |
| Rizvan Kuniev | | 2-1-0 | Russia | Jul 25, 2026 |
| Keigo Kunihara (inactive) | | 0-1-0 | Japan | Oct 7, 2005 |
| Kiichi Kunimoto (inactive) | Strasser | 3-2-0 | Japan | Jun 10, 2017 |
| Leo Kuntz (inactive) | The Lion | 0-2-0 | Unknown | Nov 28, 2015 |
| Ryan Kuse | 3rd Street Savage | 0-1-0 | United States | Aug 22, 2026 |
| Guram Kutateladze (inactive) | Georgian Viking | 2-3-0 | Georgia | Mar 22, 2025 |
| Kwan Ho Kwak (inactive) | | 0-2-0 | South Korea | Jun 17, 2017 |
| Mike Kyle (inactive) | MAK | 2-1-0 | United States | Feb 5, 2005 |