UFC Fighters: O
47 fighters with a last name starting with O
- Jake O'BrienLight Heavyweight · 15–4
- T.J. O'BrienLightweight · 0–2 in the UFC
- Sean O'ConnellLight Heavyweight · 21–10
- Sean O'MalleyBantamweight · 20–3
- Chuck O'NeilWelterweight · 0–1 in the UFC
- Casey O'NeillWomen's Flyweight · 12–2
- Brendan O'ReillyLightweight · 6–3
- José OchoaFlyweight · 2–2 in the UFC
- Volkan OezdemirLight Heavyweight · 21–8
- Kaan OfliFeatherweight · 3–2 in the UFC
- Trey OgdenLightweight · 3–3 in the UFC
- Andy OgleFeatherweight · 9–6
- Koji OishiWelterweight · 0–2 in the UFC
- Yushin OkamiWelterweight · 39–15
- Bolaji OkiLightweight · 2–3 in the UFC
- Aleksei OleinikHeavyweight · 62–18–1
- Cezary OleksiejczukMiddleweight · 1–0 in the UFC
- Michał OleksiejczukMiddleweight · 22–10
- Alex OliveiraWelterweight · 26–20–1
- Charles OliveiraLightweight · 37–11
- Ednaldo OliveiraLight Heavyweight · 0–2 in the UFC
- Maria OliveiraWomen's Strawweight · 1–2 in the UFC
- Michael OliveiraWelterweight · 1–0 in the UFC
- Rafaello OliveiraLightweight · 17–8
- Ravena OliveiraWomen's Flyweight · 0–4 in the UFC
- Saimon OliveiraBantamweight · 0–4 in the UFC
- Vinicius OliveiraFeatherweight · 24–4
- Wendell OliveiraWelterweight · 0–2 in the UFC
- Felipe OlivieriLightweight · 0–1 in the UFC
- Gadzhi OmargadzhievWelterweight · 0–2 in the UFC
- Alan OmerFeatherweight · 0–2 in the UFC
- Daniel OmielańczukHeavyweight · 26–14–1
- Michihiro OmigawaFeatherweight · 19–15–1
- David OnamaFeatherweight · 14–3
- Charlie OntiverosLightweight · 0–3 in the UFC
- Myktybek OrolbaiWelterweight · 16–3–1
- Brian OrtegaFeatherweight · 16–5
- Dustin OrtizFlyweight · 20–9
- Tito OrtizLight Heavyweight · 21–12–1
- Ode' OsbourneFlyweight · 13–9
- Nick OsipczakWelterweight · 6–3
- Mehemmedeli OsmanliBantamweight · 0–1 in the UFC
- Nissen OsterneckMiddleweight · 0–1 in the UFC
- Rachael OstovichWomen's Flyweight · 4–6
- Zak OttowWelterweight · 20–8
- Alistair OvereemHeavyweight · 47–19
- Alptekin ÖzkılıçFlyweight · 9–5
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