The Las Vegas-based promotion recently confirmed the new flyweight booking after it was initially announced by All In Sports Management. UFC 305 takes place at the RAC Arena in Perth, Australia, and is headlined by a middleweight title tilt between Dricus Du Plessis and Israel Adesanya.
Santos will make a quick turnaround after appearing at UFC on ESPN 59 on July 13, when she defeated Mariya Agapova via first-round submission. The 24-year-old Brazilian has won five straight contests, including three in UFC competition.
O’Neill, meanwhile, began her professional tenure with nine consecutive triumphs. After winning her first four Octagon appearances, “King” has dropped back-to-back fights against Jennifer Maia and Ariane Lipski.