Purpose: This study aimed to verify index of autonomous functioning, IAF (Weinstein, Przybylski, & Ryan, 2012) via two independent samples using exploratory and confirmatory factor analyses. Methods: Five hundred and sixteen senior middle school athletes (Mage = 16.53) were recruited. Main analyses were exploratory factor analysis, confirmatory factor analysis and simultaneous multigroup covariance analyses. Results: The factorial validity of IAF was demonstrated as good and the invariance between male and female athletes was also substantiated in this scale. Conclusion: According to these results, IAF had a good psychometric property and was suitable to measure athletes’ autonomous functioning in Taiwan.