The purpose of this study was to investigate the activities of the serratus anterior (SA) and upper trapezius (UT) muscles during scapular protraction exercise with a dumbbell. Twenty-one healthy subjects with no medial history of shoulder pain or upper extremity disorders were recruited for this study. Subjects performed scapular protraction at $90^{circ}$ and $130^{circ}$ shoulder flexion with a dumbbell in supine and standing positions. The activities of the SA and UT were measured via surface electromyography (EMG) during 4 scapular protraction exercises. A 2 (angle) ${ imes}$ 2 (position) repeated-measures analysis of variance (ANOVA) was used to compare the normalized activities of the SA and UT and the UT/SA ratio. The results showed that activities of both the SA and UT were the highest for the scapular protraction exercise at $130^{circ}$ shoulder flexion in the standing position. However, the UT/SA ratio was the lowest for the exercise at $90^{circ}$ shoulder flexion in supine position. Therefore, for selective activation of the SA muscle, we recommend performing the scapular protraction exercise with a dumbbell in the supine position at $90^{circ}$ shoulder flexion.