PURPOSE: The purpose of this study was to compare how the shoulder height and respiratory function are affected by applying shoulder stabilization exercises and core stabilization exercises that are effective for strengthening the trunk muscles and postural stability for adults with a round shoulder posture (RSP). METHODS: The participants were 28 young adults with RSP. They were assigned randomly to two groups: shoulder stabilization exercise and core stabilization exercise. They performed the exercises for 30 minutes twice a week for four weeks. They measured the shoulder height and respiratory function before and after exercise. RESULTS: No significant difference in shoulder height was found between the groups. A significant decrease in shoulder height was found in the shoulder stabilization exercise group after exercise. The core stabilization exercise group showed a significant decrease after exercise. In respiratory function, no significant difference was found between the groups. The forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were increased significantly in the shoulder stabilization exercise group before and after exercise. The FEV1, FEV1/FVC, and peak expiratory flow were significantly higher in the shoulder stabilization exercise group after exercise than in the core stabilization exercise group. CONCLUSION: Shoulder stabilization exercise and core stabilization exercise improved the postural alignment and pulmonary function, and the exercises could be helpful in shoulder rehabilitation as well as the clinical part of the treatment of rounded shoulder posture.