[Purpose] The purpose of this study was to compare shoulder stabilization muscle activities according to postural changes during flexi-bar exercise. [Subjects] The subjects included 18 students (10 males, 8 females) at B University. [Methods] The subjects performed the following flexi-bar exercises: 1) medio-lateral oscillation with the 90° shoulder abduction, with the hand in the neutral position; 2) dorso-ventral oscillation with 90° shoulder flexion, with the hand in the neutral position; 3) superior-inferior oscillation with 90° shoulder flexion, with the 80° hand pronation. [Results] The activity of the serratus anterior showed significant differences between each position; however, activities of the upper trapezius and middle trapezius were not significantly different. [Conclusion] The results of this study indicate that posture control is important for selective strengthening of the serratus anterior muscle during flexi-bar exercises.