Previous studies have shown that core stability exercises have a significant effect on balance. The purpose of this study was to investigate the effects of core stability exercises weeks number on the balance functions of athletes with a history of anterior cruciate ligament injury. forty-four female athletes, 21 with a healthy knee, and 21 with a history of anterior cruciate ligament injury were randomly selected. The number of weeks of core stability exercises included one week, four, and eight weeks, and the subjects performed the training protocol three times a week and each session was 45 minutes. In this research, before and after the completion of training weeks the leg stance time test was used to evaluate static balance, and the Y test was used to evaluate dynamic balance. Analysis of variance with repeated measurements was used to determination of the effect of the number of weeks of core stability exercises was used within and between groups. The results showed that the number of core stability exercises weeks number had a significant effect on the static balance and these effects were different between the two groups (p<0.05). Also, findings showed that the core stability exercise weeks number had a significant effect on dynamic balance, and comparing the results was different between the two groups (p<0.05). Regarding findings of this study suggested that optimal core stability exercise weeks number be considered in the design of training protocols.