Guilherme Viana (born May 13, 1986) is a Brazilian mixed martial artist formerly competing in Bellator's Light Heavyweight division. A professional competitor since 2012, Viana was a contestant on . He currently competes as a bare-knuckle boxer in Bare Knuckle Fighting Championship.
Viana began his professional MMA career in March 2012. He quickly compiled a 4âÂÂ1 record, with his lone loss being against former UFC and Bellator competitor Rodney Wallace, before appearing on .
In February 2014, Viana was revealed as one of the contestants on , competing as a heavyweight. In the fight to get into the house, Viana lost to eventual winner of the heavyweight tournament Antônio Carlos Júnior via TKO in the first round, thus being eliminated from the competition.
Viana made his Bellator and United States debut against nine-time UFC veteran Francis Carmont at Bellator 135 on March 27, 2015. Viana lost the fight via unanimous decision.
Viana faced another UFC veteran in Houston Alexander at Bellator 146 on November 20, 2015. He won the fight via TKO due to a doctor stoppage following the conclusion of the second round.
Viana then faced Philipe Lins at Bellator 159 on July 22, 2016. After a conservative first round from both fighters, Viana lost the fight via TKO due to punches in the second.
Viana made his Bare Knuckle Fighting Championship debut against Aleem Whitfield on December 20, 2025 at BKFC Fight Night 33. He won by knockout at the end of the second round.
Viana faced Juan Figuerva on January 17, 2026 at . He won the fight by knockout at the end of the first round.
Viana faced Joseph White on March 28, 2026 at BKFC Fight Night 35. He lost the fight by knockout in the first round.
Viana has a brother, who is also a mixed martial artist.
|- |Loss |align=center|9âÂÂ4 |Rasul Magomedov |Decision (unanimous) |PFL 10 (2025) | |align=center|3 |align=center|5:00 |Hollywood, Florida, United States | |- |Win |align=center|9âÂÂ3 |Hassan Graham |KO (punches) |Combat Zone 86 | |align=center|1 |align=center|0:53 |Manchester, New Hampshire, United States | |- |Win |align=center|8âÂÂ3 |Terrance Jean-Nacques |TKO (punches) |Combat Zone 83 | |align=center|2 |align=center|3:05 |Manchester, New Hampshire, United States | |- |Loss |align=center|7âÂÂ3 |Philipe Lins |TKO (punches) |Bellator 159 | |align=center|2 |align=center|1:13 |Mulvane, Kansas, United States | |- |Win |align=center|7âÂÂ2 |Houston Alexander |TKO (doctor stoppage) |Bellator 146 | |align=center|2 |align=center|5:00 |Thackerville, Oklahoma, United States | |- |Loss |align=center|6âÂÂ2 |Francis Carmont |Decision (unanimous) |Bellator 135 | |align=center|3 |align=center|5:00 |Thackerville, Oklahoma, United States | |- |Win |align=center|6âÂÂ1 |Julio Cesar dos Santos |TKO (punches) |The Hill Fighters 2 | |align=center|2 |align=center|0:46 |Gramado, Brazil | |- |Win |align=center|5âÂÂ1 |Cristiano Monteiro |Submission (rear-naked choke) |Shooto Brazil 47 | |align=center|1 |align=center|N/A |Rio Bonito, Brazil | |- |Win |align=center|4âÂÂ1 |Ricardo Silva |TKO (punches) |Watch Out Combat Show 28 | |align=center|1 |align=center|N/A |Gramado, Brazil | |- |Loss |align=center|3âÂÂ1 |Rodney Wallace |Decision (split) |Iron Fight Combat 2 | |align=center|3 |align=center|5:00 |Aracaju, Brazil | |- |Win |align=center|3âÂÂ0 |Ed Carlos |TKO (punch) |Iron Fight Combat 1 | |align=center|1 |align=center|1:19 |Feira de Santana, Brazil | |- |Win |align=center|2âÂÂ0 |Gustavo Gussem |TKO (punches) |Watch Out Combat Show 19 | |align=center|1 |align=center|1:50 |Rio de Janeiro, Brazil | |- |Win |align=center|1âÂÂ0 |Eduardo Camilo |Submission (armbar) |MMA Against Dengue 2 | |align=center|1 |align=center|3:51 |São Gonçalo, Brazil |
|- |Loss |align=center|2âÂÂ1 |Joseph White |TKO | | |align=center|1 |align=center|0:34 |Uncasville, Connecticut, United States | |- |Win |align=center|2âÂÂ0 |Juan Figuerva |KO | | |align=center|1 |align=center|1:59 |Uncasville, Connecticut, United States | |- |Win |align=center|1âÂÂ0 |Aleem Whitfield |KO | | |align=center|2 |align=center|1:59 |Uncasville, Connecticut, United States |