Objective: This study examined alterations in ankle eversion/inversion strength and postural control in chronic lateral ankle instability (CLAI). Methods: Twenty-three CLAI patients and 14 matched controls underwent isokinetic strength testing at 30°/s, 60°/s, and 90°/s (peak torque/body weight: PT/BW). Postural control was assessed via center-of-pressure (COP) trajectory length and peripheral area during eyes-open and eyes-closed single-leg stance. Results: The CLAI group demonstrated significantly lower eversion PT/BW across all angular velocities versus controls (p<0.05). Inversion PT/BW was not significantly different for the group effect (p>0.05). The eversion-to-inversion strength ratio was consistently lower in CLAI (p<0.05). No between-group differences in COP metrics occurred during eyes-open stance (p>0.05). However, with eyes closed, the CLAI group exhibited significantly longer COP trajectory [107.52 (94.90,118.70) cm vs. 93.75 (83.09,95.25) cm] and larger peripheral area [8.34 (5.73,12.90) cm² vs. 5.92 (5.05,6.88) cm²] (p<0.05). Conclusions: CLAI is characterized by eversion muscle weakness and an impaired eversion-to-inversion strength ratio. Postural control deficits manifest primarily under visual deprivation, suggesting proprioceptive impairment, though visual input enables partial compensation during eyes-open conditions.