This study aimed to examine the mediating role of mental toughness (confidence, control, and constancy) in the relationship between personality traits (neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness) and competitive anxiety (cognitive anxiety, somatic anxiety, and competitive self-confidence) among female martial artists. This descriptive–correlational study included a sample of 82 female martial artists (mean age = 21.45 years) from Ahvaz. Data were collected using the NEO Five-Factor Inventory, the Sports Mental Toughness Questionnaire, and the Competitive State Anxiety Inventory, and analyzed using Pearson correlation coefficient and a bootstrap-based mediation model. Findings indicated that mental toughness functions as a mediating mechanism in transmitting a substantial portion of the effects of personality traits on competitive anxiety. Specifically, personality traits primarily influenced competitive anxiety and self-confidence through mental toughness components, and in some cases had direct effects. Neuroticism, via reduced confidence, was associated with increased anxiety and decreased self-confidence; extraversion primarily operated through control; agreeableness and openness to experience through constancy; and conscientiousness via a combination of control and constancy, all contributing to reduced anxiety and enhanced competitive self-confidence. The statistical significance level for all relationships in this study was p < 0.05, and significance for the indirect paths was confirmed by the confidence interval not containing zero. These results suggest that mental toughness serves as a mediator between personality and competitive anxiety, and targeted enhancement of its components, as developable psychological capacities, may provide practical strategies for sport psychologists and coaches to reduce competitive anxiety and improve performance in female athletes.