[Purpose] This study investigated the differences in shoulder muscles activities during shoulder abduction between a forward shoulder posture group and asymptomatic group. [Subjects] Seven males with forward shoulder posture (FHS) and seven asymptomatic males were recruited. [Methods] We measured the upper and middle trapezius (UT and MT), serratus anterior (SA), and clavicle portion of the pectoralis major (cPM) in the right side during shoulder abduction. [Results] The activities of the UT and cPM in the FHS group were significantly more increased when compared with the asymptomatic group. The activities of the MT and SA in the FHS group were significantly more decreased when compared with the asymptomatic group. [Conclusion] We suggest that forward shoulder posture may become a potential risk factor evoking the various shoulder disorders.