Japan Ham debuted against Japanese MMA veteran Hisae Watanabe on at
Deep 28 Impact, upsetting the favorite Watanabe by winning via unanimous decision. Ham was defeated by Miku Matsumoto via
triangle choke submission on at
clubDeep Toyama: Barbarian Festival 6. Ham rebounded back from her first loss with a unanimous decision victory over Ayumi Saito on at ''
Smackgirl 2007: Queens' Hottest Summer
. On at Smackgirl 7th anniversary: Starting Over
, Ham challenged Smackgirl Lightweight Champion Yuka Tsuji for her title, losing by unanimous decision in a match that Tsuji completely dominated. On , Ham participated in the Smackgirl World ReMix Tournament 2008 Opening Round
, where she defeated Saori Ishioka by unanimous decision. In the tournament semi-finals on , Abe Ani Combat Club star Megumi Fujii handed Ham her third professional defeat by submitting her with an armbar in the Smackgirl World ReMix Tournament 2008 Second Round''. After a year without fights in MMA, Ham made her debut with MMA promotion Jewels and earned another victory on by defeating Misaki Takimoto by unanimous decision at
Jewels 5th Ring. Ham next participated at
Jewels 9th Ring in the first round of the inaugural Jewels Lightweight Queen Tournament, held to crown the first Jewels Lightweight Champion, where she defeated
Mai Ichii by unanimous decision on . Ham was slated to compete at
Jewels 10th Ring, but since she decided to participate in two kickboxing matches with conflicting dates, Jewels released her. Jewels later announced that she would still participate in the semi-finals of the Lightweight Queen Tournament at
Jewels 11th Ring. Ham faced
Mika Nagano in the semi-finals and defeated Nagano by split decision. In the tournament final later that night, Ham was defeated by
Ayaka Hamasaki via unanimous decision. Ham had a rematch against
Saori Ishioka on at
DEEP: 52 Impact in
Tokyo, Japan. She once again defeated Ishioka by unanimous decision. On , Ham faced Anna Saito in a mixed martial arts rules match at
Gladiator 15: GI 2. Ham defeated Saito by unanimous decision. Ham faced
Mei Yamaguchi in a
Jewels vs. Valkyrie match at
Jewels 15th Ring on . She defeated Yamaguchi by unanimous decision. Ham challenged Jewels champion
Ayaka Hamasaki in a rematch at
Jewels 17th Ring on . She was defeated by TKO (corner stoppage) after the first round when she could not continue due to injury. On , Ham faced pro wrestler Ryo Mizunami at
Gladiator: Dream, Power and Hope. She defeated Mizunami by submission due to an armbar early in the first round. Ham dropped down in weight to challenge
Naho Sugiyama for the Jewels Atomweight queen title at
Jewels 24th Ring on . She defeated Sugiyama by unanimous decision to become the new Jewels Atomweight queen champion. Following Jewels' closure, Ham's title was renamed the Deep Jewels Atomweight championship. She defended the title against Sadae Numata at
Deep Jewels 2 on . Ham won the fight by unanimous decision.
Ultimate Fighting Championship In early November 2014, Seo Hee Ham signed a four-fight contract with
Ultimate Fighting Championship to join UFC's Strawweight division. She made her debut against
Joanne Calderwood at
The Ultimate Fighter: A Champion Will Be Crowned Finale on December 12, 2014. She lost the fight by unanimous decision. Ham was expected to face
Bec Rawlings on May 10, 2015 at
UFC Fight Night 65. However, Ham pulled out of the bout on April 10 and was replaced by
Lisa Ellis. After nearly a year away from the company, Ham returned to face Cortney Casey on November 28, 2015 at
UFC Fight Night: Henderson vs. Masvidal. She won the fight via unanimous decision. The win also earned Ham her first
Fight of the Night bonus award. She lost to
Danielle Taylor at
UFC Fight Night 101 on Nov. 26, 2016 via split decision and was subsequently released from the promotion.
Road FC After briefly considering retirement, Ham signed with Road FC where she became the atomweight champion with a victory over
Mina Kurobe. On December 23, 2017, she successfully defended her atomweight championship with a first round stoppage over
Jinh Yu Frey.
Rizin On June 21, 2019, it was announced Ham would face former DEEP Champion
Tomo Maesawa at
Rizin 17 on July 28, 2019. She won the fight by TKO in the first round. Next, Ham faced
Miyuu Yamamoto at
Rizin 19 on October 12, 2019. She won the fight via technical knockout in the second round. With two consecutive victories in Rizin, Ham earned a title shot against
Ayaka Hamasaki at
Rizin 20 on December 31, 2019. She won the trilogy fight via split decision, becoming the second
Rizin Women's Super Atomweight Champion. Ham vacated her Rizin Atomweight title in October 2020, as she couldn't come to an agreement with Rizin for her next fight.
ONE Championship After vacating her Rizin Atomweight title, Ham signed with
ONE Championship, where she will compete in the atomweight division. She was scheduled to take part in the ONE Atomweight Grand Prix. It was reported that Ham will face Denice Zamboanga in the quarter-final of the
ONE Women's Atomweight Grand Prix at
ONE Championship: Empower on May 28, 2021. The event was later postponed due to
COVID-19 precautions. The event was rescheduled for September 3, 2021. She won the close bout via split decision. Due to the controversy the decision stirred, the bout was placed under review but the ONE Championship committee left the result standing. Ham was scheduled to face
Stamp Fairtex in the semi-final bout of
ONE Women's Atomweight Grand Prix at
ONE Championship: Next Generation on October 29, 2021. Ham had to pull out of the bout due to injury and was replaced by alternate bout winner Julie Mezabarba. Ham was scheduled to rematch Denice Zamboanga at
ONE: X on December 5, 2021. Their rematch was later postponed to March 6, 2022. Ham failed the hydration test the day before the fight, and was given until midnight to pass. Ham was able to pass the test in the mandated time and won the fight by unanimous decision. Ham was scheduled to face
Itsuki Hirata at
ONE 163 on November 18, 2022. However, Hirata missed weight and failed the hydration test, and the match was scrapped after Ham declined a catchweight bout due to Hirata's history of missing weight. The pair was rescheduled for March 25, 2023, at
ONE Fight Night 8. She won the fight via unanimous decision. Ham faced
Stamp Fairtex at
ONE Fight Night 14 on September 29, 2023. The bout was originally scheduled to be for the interim
ONE Women's Atomweight title, however after reigning champion
Angela Lee announced her retirement during the event, the fight became for the vacant undisputed title. Ham lost the fight via technical knockout in the third round. == Kickboxing career ==