Isometric positioning of the ACL graft is an important consideration in successful reconstruction of the ACL-deficient knee. The purpose of this study is to get a certain guideline in the endoscopic one-tunnel technique of anterior cruciate ligament reconstruction by measuring the skin angle and determine the degree of minimum flexion of the knee joint during femoral tunneling and interference screw fixations. To get the guide lines, first we get the tibial tunnel angle parallel to the Blumensaat's line from fully extended lateral knee joint radiography. Secondly measure the differences between angles of the femur-tibia shaft and anterior thigh-leg skin. Then measure the minimum femur-tibia flexion angle does not perforated the posterior cortex of the distal femur during femoral tunneling. Intraoperative measuring the angle between interference screw guide pin and tibial tunnel to get the parallelism of the femoral tunnel and interference screw. The results were as follows; The average femur-tibia shaft angle with 30degrees anterior thigh-leg skin angle was 30.2±1.75degrees, with 45degrees was 45.2±1.23degrees, with 60degrees was 61.9±4.23degrees, with 75degrees was 78.6±2.62degrees, with 90degrees was 97.8±3.96degrees. Predetermined sagittal tibial tunnel vector on the 0degrees extension knee joint lateral radiographs were applied to the several knee joint dynamograms. The mean minimum flexion angle of the femur-tibia shaft that doesn't perforate the posterior cortex of the femur was 45±1.58degrees (male), 44.5±4.97degrees (female). The average angle between interference screw guide pin and tibial tunnel was 23.0±2.23degrees. The findings of the present study suggest that anterior thigh-leg skin angle can be used instead of the true femur-tibia shaft angle. Less knee flexion angle makes good arthroscopic view during the tibio-femoral tunneling and interference screw fixation.