Purpose : The purpose of this study was to find the effect of ankle joint angle on knee extensor electromyographic activity following knee extension exercise. Methods : Ten male university students participated in the study. The subjects performed isometric maximal voluntary knee extensor contractions (MVC) and knee extensor EMG activity measured in with three different ankle joint angle. The EMG activity of rectus femoris(RF), vastus medialis(VM), vastus lateralis(VL) were measured using surface electromyography. Results : EMG activity of vastus lateralis following the change of ankle joint angle was shown statistically significant difference. Conclusion : Ankle plantar flexion position increase EMG activity of vastus lateralis during knee extension exercise.