While the cruciate ligament has a profuse vascular response following injury, spontaneous repair does not occur. This may result from the fact that synovial fluid dilution of the hematoma following injury prevents the formation of a fibrin clot and thus the initiation of the healing mechanism. Another theory suggests that the dynamic nature of the fascicles of the anterior cruciate ligament(ACL) through even small ranges of motion prohibits spontaneous union to these fibers. But we experienced two cases of spontaneous healing of partially injured ACL. Initially they showed more than grade II anterior instability. 6 mm difference by stress roentgenographs(pull view) and difference of 8 mm by KT 1000TM arthrometer between the ACL injured knee and normal side knee. Lax, nearly complete tear of ACL and synovial bleeding were noted during arthroscopic examination but the continuity of synovial membrane was seemed to be intact. These cases were treated by conservative management rather than reconstructive procedure. Postoperatively they showed excellent clinical results, no anterior instability and unlimited athletic activity. Based on our clinical experience. we think that cruciate ligament has the spontaneous healing potential in acute stage and middle aged patient. We consider the microfracture technique and initial immobilization for accelleration of healing response of the ACL.