Fast facts
- Division: Women’s bantamweight (MMA); former ONE women’s strawweight (Muay Thai)
- Record: 2-0 in pro MMA; 31-5-1 in Muay Thai before signing with ONE Championship
- Nationality: Swedish (born in Sundbyberg)
- Team/gym: Diaz Combat Sports, per Combat Press; trained and lived at Fairtex Gym in Pattaya from October 2019 until 2025
- Notable wins: Jackie Buntan, Allycia Rodrigues, Diandra Martin, Sawsing Sor Sopit, Miranda Barber, Maya Stewart
The family went home to Sweden, and the 15-year-old stayed in Thailand.
That’s the moment I keep coming back to with Smilla Sundell. Her family had moved to Ko Samui when she was 12 because of her parents’ work, and there wasn’t much for a kid to do on the island in the way of organized sport. So she and her younger sister started showing up at a place called Yodyut Muay Thai. She’d done karate since she was five, for self-defense, and she’d first tried Muay Thai on a vacation to Thailand at 10 or 11. Ko Samui turned a holiday curiosity into a daily routine. When her parents went back to Sweden, she decided the routine was her life.
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Eventually the island ran short of opponents for her. She’d been watching Stamp Fairtex, and in October 2019 she moved to Pattaya and joined Fairtex Gym, where she lived and trained for the next six years. Gym kids who live in the camp know a specific kind of upbringing: the fighters are your neighbors, the trainers are your guardians in practice if not on paper, and a bad sparring day follows you to dinner. Sundell grew up inside that.
The teenager with the belt
By early 2021, at 16, she was ranked the No. 1 female featherweight in the world by WBC Muaythai. Her Thai résumé included wins over the decorated champion Sawsing Sor Sopit, over Ponpan Por.Muengpetch, and over a male fighter, Bongsak Sitpholek. She signed with ONE Championship in 2021 carrying a 31-5-1 record.
Her ONE debut came on Feb. 25, 2022, at ONE: Full Circle against Australia’s Diandra Martin, and it was her first fight in four-ounce MMA gloves, which are smaller than what Muay Thai fighters usually wear. She stopped Martin in Round 3. Less than two months later, on April 22, 2022, at ONE 156, she beat Jackie Buntan by unanimous decision for the inaugural ONE women’s strawweight Muay Thai title. She was 17 years and five months old, the youngest person ever to win a world title in Muay Thai, and she took home a $50,000 Performance of the Night bonus for the trouble. ONE named her its Super Series Female Fighter of the Year for 2022.
She kept moving. On May 26, 2023, at ONE Friday Fights 18, she made her kickboxing debut and beat Milana Bjelogrlić by unanimous decision. Then, on Sept. 29, 2023, at ONE Fight Night 14, she defended her belt against Allycia Rodrigues, who held the ONE atomweight Muay Thai title. Champion against champion. Sundell finished her by TKO in Round 3 and banked a second $50,000 bonus.
That Rodrigues win is the defining fight of her ONE run, for my money. Buntan made her a record holder. Rodrigues proved she was a champion who could beat other champions.
The scale
The second defense, against Natalia Diachkova at ONE Fight Night 22 on May 4, 2024, is where the story turns. At an unofficial check two and a half hours into weigh-ins, Sundell came in at 127.7 pounds. Her official weight was 126.5, a pound and a half over the strawweight title limit. ONE stripped her, and only Diachkova could leave with the belt. The fight went ahead and ended by technical knockout in the second round, but the title Sundell had won as a 17-year-old was gone.
On Aug. 19, 2025, reports surfaced that ONE had removed her from its roster. The reason was size: her weight had gone past the promotion’s heaviest women’s division.
It’s easy to sneer at weight misses, and plenty of people do. This one deserves a little more patience. She signed with ONE as a 16-year-old and won its belt at 17. Teenagers grow. A body that made strawweight in 2022 had no obligation to keep making it into her 20s, and by 2025 the promotion simply didn’t have a place for the body she had.
Starting over in four-ounce gloves
On Oct. 26, 2025, the Las Vegas promotion Tuff-N-Uff announced it had signed her. Her planned pro MMA debut against Zurina Turrey at Tuff-N-Uff 150 on Dec. 12, 2025, fell through when Turrey wasn’t medically cleared.
She debuted instead on Jan. 22, 2026, at Tuff-N-Uff 151 in Las Vegas, and beat Miranda Barber by TKO with knees and elbows at 4:54 of Round 1. Those are Fairtex weapons, the tools a kid picks up through years of clinch work in Pattaya, and they translated to the cage on her first try. Dana White praised the performance on social media afterward. On June 5, 2026, at Tuff-N-Uff 154, she fought Maya Stewart at bantamweight and won by referee stoppage from strikes at 1:28 of Round 2.
Two fights, two finishes. Combat Press described both knockouts as brutal and called her the dark horse of the week. It also lists her team as Diaz Combat Sports, a long way geographically and culturally from the Pattaya camp where she spent her adolescence.
I’ll be the cautious one here, because I’ve watched too many prospects get coronated on a short record. Two regional wins tell you her striking survives smaller gloves and a cage. They don’t tell you what happens when someone puts her on her back for five minutes, and the sources don’t show anyone having tried. That test is coming, and nobody, including her, knows the answer yet.
Tuesday at the Apex
What’s next is immediate. On Tuesday, Oct. 13, Sundell (2-0) meets Aline Pereira (3-2) in the women’s bantamweight co-feature of the Dana White’s Contender Series Season 10 finale at the Meta Apex in Las Vegas, streaming on Paramount+ at 7 p.m. ET. Both women weighed in at 135 pounds on Monday, and MMA Junkie posted their face-off on X afterward. For a fighter who lost a world title on a scale, a clean weigh-in at a division that fits her matters.
Pereira is the younger sister of former two-division UFC champion Alex Pereira. She’s a former GLORY kickboxer and the current Karate Combat flyweight champion, and she has won her last two MMA fights, one of them over Canada’s Jade Masson-Wong on the Rousey vs. Carano card on Netflix earlier this year. Combat Press lists her at 35 and Cageside Press at 36; either way, she’s roughly 15 years older than Sundell, who is 21.
Cageside Press pointed out that the women’s bantamweight division badly needs fresh blood and flagged Sundell’s short MMA record as a question mark. Combat Press noted how thin the women’s 135-pound class is and picked Sundell to win. Robinhood has even listed a prediction market on the fight.
Two strikers, a combined five pro MMA fights, and a UFC contract potentially on the table. Sundell has been fighting for money since she was a child on an island where there was nothing else to do, and she has already been the youngest champion in her sport’s history once. On Tuesday night she gets a chance to start that climb again, this time at 135 pounds.
