This study was conducted to examine the effect of monthly telephone message reminders after training on women's beliefs and practice behaviours regarding breast self-examination. This randomized controlled study was conducted with 83 women aged 20-69 years living in Turkey between September 2021 and July 2022. Women were randomly assigned (1:1) to the intervention (n = 41) or control group (n = 42), both groups received online breast self-examination training, and the intervention group received monthly reminders on their mobile phones for 3 months. Participants completed the Champion's Health Belief Model Scale and breast self-examination practice evaluation form at baseline and 3 months after intervention. After the intervention, the mean scores of the benefits and self-efficacy subscales of Champion's Health Belief Model Scales were significantly higher in the intervention group compared to the control group, and the mean score of barriers was lower. The rate of performing breast self-exam regularly and at the appropriate time was higher in the intervention group. The rate of forgetting to perform breast self-examination was higher in control group. A monthly reminder message may be recommended to increase women's belief in breast self-examination and increase regular practice.