Purpose: This study was done to evaluate the effects of Yoga exercise on improvements in physical flexibility, posture management behavior, and self-efficacy in adolescents. Method: In this study, the design was a quasi-experimental research design with a one group pretest-posttest design. Participants were 32 students from one high school in Busan Metropolitan City, Korea, who did not engage in regular aerobic exercise and were willing to participate in this study. Yoga exercise was conducted for 70 minutes twice a week for 15 weeks. The data were collected from March 16 to June 22, 2004. The data were analyzed using descriptive statistics, and paired t-test with SPSS Win 12.0. Results: Trunk flexibility, posture management behavior, and self-efficacy significantly increased after the yoga exercise. Conclusion: Yoga exercise is recommended as a useful nursing intervention that could help prevent spinal-curvature-related disorders among adolescents.