Purpose: This pilot study aimed to assess the feasibility, preliminary efficacy, and effects of a mobile app healthcare coaching program developed based on self-regulation theory among youths with type 1 diabetes.Methods: A mixed-method design was utilized. Participants were randomly assigned into intervention (n=23, 12-week coaching program) or control groups (n=16, usual care). Pre- and post-intervention assessments included self-efficacy, diabetes management behavior, and health outcomes (quality of life, depression, and HbA1c). Quantitative data were analyzed with SPSS/WIN ver. 26.0. The narrative information from the participants in the healthcare coaching program underwent content analyzed.Results: The intervention group had significantly lower depression scores (t=2.57, p=.014) than the control group. No significant differences were observed in self-efficacy, diabetes management behavior, and health outcomes between the two groups. The average frequency of health behavior monitoring per week among the participants was 1.86±1.60. The qualitative findings indicated that participants perceived improved diabetes self-management with the intervention; however, challenges during vacations, dietary control difficulties, and a lack of disease awareness were identified.Conclusion: The healthcare coaching program improved psychological aspects for youth with type 1 diabetes. Further research is needed to develop and implement mobile app interventions aimed at enhancing compliance with diabetes management in pediatric and adolescent populations.