This study was conducted to evaluate the isokinetic muscle function of ankle eversion and inversion of 30 amateur athletes with chronic ankle instability. The purpose of this study is to provide basic exercise prescription data for patients with chronic ankle instability by evaluating the maximum muscle strength, muscular endurance, muscle fatigue and muscle function ratio of ankle eversion and inversion difference between the involved and non-involved. Isokinetic muscle function evaluation was performed 4 repetitions at 60°/ sec angular velocity and 25 repetitions at 180〬 / sec angular velocity on the affected to calculate the peak torque and total work. Independent t-test was performed to examine the difference in the maximum muscle strength, muscular endurance, muscle fatigue, and muscle function ratio of ankle eversion and inversion to the amateur athletes with chronic ankle instability. Involved in chronic ankle instability was lower in invertor (p<.05) and evertor (p<.01) than non-involved and statistically significantly lower invertor and evertor muscular endurance(p<.05). There was no statistically significant difference in the muscle fatigue and muscle function ratio of ankle eversion and inversion between the involved and non-involved. The results of this study are as follows. First, the chronic ankle instability of amateur athletes may be reduce the maximum muscle strength and endurance of the invertor and evertor ankles. Second, the chronic ankle instability of amateur athletes may not affect the muscle fatigue and muscle function ratio of ankle eversion and inversion between the involved and non-involved.