The flexors/extensors imbalance can be a cause knee instability and therefore lead to progression of osteoarthritis. The isokinetic evaluation of the strength of flexors after the autoplastic reconstruction the anterior cross-shaped (cruciate) ligament (ACL) is of primary importance bearing in mind that certain authors have reported a persistent deficiency in flexor strength after surgery. Objective. The purpose of the present study was to objectively evaluate the isokinetic function of the knee during each treatment stage and estimate the influence of harvesting semitendinosus/gracilis tendon (SGT) on the knee flexion. Patients and methods. During the period from 2012 to 2014, a total of 44 patients (20 women and 24 men) presenting with ACL rupture were available for the examination. All the patients underwent the isokinetic evaluation of the knee function before operation, 6—8 weeks and 3—4 months after the arthroscopic ACL reconstruction with the use of the SGT graft. The patients were divided into two groups. The first group was comprised of 22 subjects who were treated in accordance with the standard protocol of therapeutic physical exercises starting from week 6 after the initiation of the physiotherapeutic rehabilitative measures. The second group consisted of 22 patients who had to perform the isokinetic training within 6—8 weeks after surgery. Results. The results of the study indicate that all the patients suffering injuries to the anterior cross-shaped ligaments had well apparent flexor/extensor imbalance. In those of the first group, the flexor imbalance amounted to 25—35% while the extensor imbalance was 10—15% within 3-4 months after the surgery. The second group showed a 10—15% flexor imbalance and 2—5% extensor imbalance after 3—4 months. Conclusion. The isokinetic testing provides a tool for the objective evaluation of the knee function. It helps to reveal the high effectiveness of isokinetic rehabilitation protocol leading to the recovery of the patients within 3—4 months after the surgery. It can be assumed based on the results of the present study that harvesting of the semitendinosus/gracilis tendon does not exert any negative influence on the knee flexion strength given the rehabilitation program includes the isotonic training protocol.