Objectives: The purpose of this study was to investigate the muscle activities of lower extremity according to the different angles of knee joint flexion when performing wall-squat on an unstable surface. Methods: 23 adults in their 20s participated in the study. Participants were randomly assigned the order of knee angles and took MVIC(maximal voluntary isomertric contraction) measurements before squats. Surface EMG(electromyography) data were collected from six muscles in the lower extremity, and wall-squat were performed according to three knee angles(60° flexed, 90° flexed, 120° flexed, respectively). Results: There were significant differences by knee angle in rectus femoris, vastus medialis, vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior. The muscle activity of rectus femoris, vastus medialis, biceps femoris and gastrocnemius was lower at 60° compared to 90° and 120°, and there was no significant difference between 90° and 120°. Vastus lateralis and tibialis anterior showed the highest muscle activity at 120° compared to 90° and 60°, followed by 120°, 90°, and 60°. Conclusions: During wall-squat exercise, which are mainly aimed at strengthening tibialis anterior and vastus lateralis, the knee flexion angle of 120° might be considered the most effective degree.