Abstract：This study aimed to characterize the sex differences and fitness determinants of dynamic balance in high school taekwondo players. Thirty male and 25 female high school taekwondo players were participated in this study. The measurements of stature, weight, and a battery of fitness tests, including vertical jump, sit-and-reach, hexagon agility test and visual reaction time of each player were recorded. In addition, individual dynamic balance was assessed by the Y-balance test (YBT), which requires the subject to stand unilaterally and use the free leg to reach as far as possible in anterior (A), posterior-medial (PM) and posterior-lateral (PL) directions. The reach distances of the dominant and non-dominant legs were then normalized with the length of leg. A two-way mixed model analysis of variance was performed to examine the interaction of sex and legs on the YBT scores, and a multiple stepwise regression analysis was performed to verify the predictors. The results showed that males performed better in the YBT than females, and symmetrical performance of dynamic balance of two legs was found in both male and female players. The YBT scores were significantly correlated to the vertical jump, stature, age and agility. Stepwise regression analysis showed that 40.8% of the variance of the YBT score of non-dominant leg could be explained by vertical jump and stature, and 35.2% of the variance of the YBT score of dominant leg could be explained by stature and age. Our study concludes that sex differences in YBT performance was ascribed primarily to variations in strength and kinematics of the lower extremities of male and female taekwondo players. (Full text)