Mia Rosales St. John (born June 24, 1967) is an American professional boxer and former World Boxing Council (WBC) champion in the super welterweight division.

On November 9, 2001, she lost her first fight to Rolanda Andrews with a TKO in the second round, St. John's first contest after parting with Top Rank.

[11] St. John turned to trainers Eduardo and Roberto Garcia to learn proper punching techniques, footwork, and defensive strategies.

St. John, coming up two weight classes, lost the bout but fought toe-to-toe with Martin all ten rounds for a credible performance.

St. John won by unanimous decision, earning the International Female Boxers Association lightweight world title.

She also spoke at the Congressional Hispanic Caucus, where President Barack Obama made a speech at the CHCI's annual Gala.

Her dream of sixteen years finally materialized and at the age of 45, she captured the WBC super welter weight championship of the world.

On November 10, 2012, St. John was defeated by Tiffany Junot in Bakersfield, California, losing her WBC Female Super Welterweight Championship in a unanimous decision.

[15] On April 14, 2016, St. John had her last boxing bout in New Zealand on the Kali Reis vs. Maricela Cornejo undercard as the curtain call.

In August 2018, St. John admitted to the use of prohibited substances including steroids and masking agents in preparation for around 20 bouts, stating that "everyone does it and everyone in boxing knows it.