OBJECTIVES: This study aimed to evaluate the effect of rapid weight regain on the fight outcomes in professional mixed martial arts (MMA) athletes competing in Bellator. MATERIALS AND METHODS: Twenty fighters (16 male and four female fighters) were included in the analysis. Official weigh-in and fight-night weights were recorded, and percentage weight regain was calculated. Fighters were divided into groups based on their percentage weight regain (<
10% vs. ≥10%). Descriptive statistics were calculated, and independent t-tests and logistic regression were employed. RESULTS: The results indicated that while fighters significantly regained weight between weigh-ins and fight-night, this weight gain did not significantly (p ≥ 0.05) predict fight outcomes. CONCLUSION: These findings suggest that weight regain may not provide a competitive advantage in Bellator MMA athletes.