Purpose The purpose of this study is to compare shoulder alignment, upper trapezius muscle tone, and pulmonary function according to stretching intervention methods in adults with rounded shoulder posture.  Methods Fortytwo subjects with rounded shoulder posture were randomly divided into three groups: active stretching, passive stretching, and control. An 8minute intervention was applied a single time, and the study measured shoulder alignment, upper trapezius muscle tone, and pulmonary function tests before and after the intervention.  Results There were statistically significant differences in the pre and postvalues of body alignment and muscle tone in the active stretching and passive stretching groups. However, there was no statistical difference in respiratory function between the pre and postvalues. In the comparison between groups, body alignment showed significant differences between the active stretching group (p<.001) and the passive stretching group (p<.05) compared to the control group, as well as between the active stretching group and the passive stretching group (p<.01). Additionally, muscle tone showed a significant difference between the active stretching group and the control group(p<.05). However, there was no statistically significant difference in pulmonary function among the three groups (p>.05).  Conclusion Active stretching has been shown to be effective in adults with round shoulder posture. Therefore, if home training is applied after physical therapy at a hospital, it is expected that the round shoulder posture can be effectively improved.