Purpose: This study aimed to develop an app-based self-management program based on the transtheoretical model (TTM) for breast cancer survivors’ exercise practice, as well as to investigate the program’s effects on the stage of change for exercise, exercise self-efficacy, exercise decisional balance, exercise amount, and body composition. Methods: This non-randomized controlled study included 52 participants (26 in each of the experimental and control groups, respectively). An app-based self-management program based on the TTM was conducted with the experimental group for a 12-week period. The program comprised three components: individual coaching for each stage of change for exercise based on TTM, amount of exercise and body composition monitoring, and online self-help meetings. Results: Compared with the control group, the experimental group had significantly higher stages of change for exercise (p < .001), exercise self-efficacy (p < .001), exercise decisional balance (p = .002), exercise amount (p < .001), and body composition (body weight [p = .006], body mass index [p = .005], and body fat percentage [p = .010]) immediately and four weeks after the intervention. Conclusion An appbased self-management program based on the TTM improves exercise behaviors in breast cancer survivors and provides physical benefits.