Background: The purpose of this study was to investigate the usefulness of quadriceps exercise for improvement of knee extensor muscular function after cruciate ligament reconstruction. Methods: Participate in 18 of patients with cruciate ligament reconstruction, ACL & PCL reconstruction was 9 of patients, respectively. All subjects instructed that quadriceps exercise repeated daily, composed to QSE(quadriceps femoris setting exercise) and SLR(straight leg raises). Knee extensor muscular function was measured before and after quadriceps exercise. Initial test was measured before cruciate ligament reconstruction, and retest was measured 6month after cruciate ligament reconstruction. Results: Knee extensor muscular function significantly increased in both ACL and PCL reconstruction(P<0.05). Conclusion: The results of this study indicated that quadriceps exercise useful for improve knee extensor muscular function in patients with cruciate ligament reconstruction.