Purpose: The purpose of this study was to examine the mediating effects of athletic identity in the relationship between self-determined motivation and exercise physical activity among university students. Methods: In a cross-sectional design, 461 university students (325 males, 136 females) completed a survey assessing behavioral regulation of exercise, athletic identity, and physical activity levels. Results: Multiple regression analysis revealed that relative autonomy index and athletic identity constructs explained 26.4% of the variance in physical activity. Relative autonomy index was a significant predictor of athletic identity and physical activity. Relative autonomy index had a significant indirect effect on university students' physical actvity through importance among the athletic identity constructs. Conclusion: Relative autonomy index or self-determination index and athletic identity may be key sources of exercise and physical activity participation in university students. Especially, importance as one of athletic identity components accounts for additional variance in physical activity participation. This construct can be valuable component of exercise promotion programs for this population.