Elevated glycated hemoglobin (HbA1c) levels and longer disease duration increase the risk of complications in type 2 diabetes mellitus (T2DM), highlighting the need for continuous management. This study evaluated the 18‐month effects of the Automated Personalized Self‐Care (APSC) program on self‐care self‐efficacy, diabetes self‐care, and complication risk indices in T2DM patients through a randomized controlled trial. Participants aged 40–69 years were assigned to either an intervention group using the APSC mobile app, which provided personalized goals, automated feedback, and monthly support, or a comparison group. The final analysis included 43 engaged participants from the intervention group and 78 from the comparison group. Data were collected at baseline, 6, 12, and 18 months using structured questionnaires and medical record reviews and analyzed using generalized estimating equations. Significant effects were observed for self‐care self‐efficacy, diabetes self‐care activities, vegetable intake, HbA1c, and total cholesterol levels. The APSC program showed potential to improve long‐term self‐care and reduce complication risk in T2DM patients. Further research with a larger samples and strategies to promote long‐term engagement is needed for its integration into routine diabetes care.Trial Registration: Clinical Research Information Service: KCT0007672