Purpose: This study performed to compare degree of joint stiffness and clinical results between early and delayed reconstruction of acute anterior cruciate ligament (ACL) injuries. Materials and Methods: Thirty-four Patients who underwent ACL reconstruction between March 2008 and October 2010 enrolled this study. We divided the patient into 2 groups, early reconstruction group underwent surgery before a week, delayed reconstruction group underwent surgery after 3 weeks, before 6 weeks. All the patients underwent aggressive joint motion exercise till surgery and enrolled post operative rehabilitation program including self exercise. We checked range of motion, the Lachman test, the pivot shift test, the Lysholm score, the International Knee Documentation Committee (IKDC) score and the Tegner score to evaluate the results. Results: At the final follow up. The Lysholm score was 91.82 in the early group and 94.83 in the delayed group. All the cases were rated above B (near normal) on IKDC score (P=0.217, P=0.845). The Tegner score was 6.7 in the early reconstruction group and 7.1 in the delayed group (P=0.840), there was no difference between the groups for the range of motion (P=0.873, P=0.873), no complication such as deep vein thrombosis or infection, no difference in the Lachman test, pivot shift test (P=0.606, P=0.118). Conclusion: We could obtain satisfactory clinical results in both the early and delayed reconstruction groups of acute ACL injuries. Therefore, the early reconstruction of ACL performed before a week could be one of the treatment options for acute ACL injury.