Background: Diabetes mellitus is a chronic disease that needs long-term management. Mobile health is an emerging field that is being used for diabetes self-management. Aim: Evaluate the effect of a diabetes self-management mobile application on self-efficacy, self-care agency, and self-care management among 128 Jordanian patients with Type 1 Diabetes Mellitus. Methods: The study utilized a non-equivalent controlled groups quasi-experimental design, with 64 patients in the control and in the intervention groups. Results: There was significant improvement in mean self-efficacy in the intervention group, improved self-care agency between the groups, and improved self-care management both within the intervention group and between the groups, after controlling for self-efficacy and self-care agency. Conclusion: Using a diabetes self-management mobile application may help improve patients’ confidence in managing diabetes, and better commitment to and performance of self-care activities.