Introduction: Mobile-based applications play a leading role in changes in life-style, improve medication adherence, and provide a unique opportunity to aid patients with type 2 diabetes mellitus (T2DM) elevate their healthcare level. Therefore, we aim to design and develop a mobile-based self-care application for patients with T2DM. Methods: The present study was an applied and developmental study to design and develop a mobile-based self-care application for people living with T2DM conducted in 2020. The design and development of the T2DM self-care application were done in 2 main phases of determining the key features and capabilities, and design and development of the T2DM self-care mobile app. Results: We identified the main model and a set of capabilities and features for the T2DM self-care application. By content analysis on 32 different applications and a previous study by the author, 18 features were extracted for the T2DM self-care mobile app. JAVA programming languages were used to design T2DM applications. Moreover, because of the cost-effectiveness, the Android operating system (AOS) was selected as a platform, and because of the widespread use of smartphones; these phones were chosen as the format of T2DM self-care application. Conclusions: In this study, we design and develop a mobile-based self-care application for patients with type 2 diabetes that shows potential in solving the shortcomings of mobile apps for diabetes care. By utilizing the T2DM self-care mobile app we are able to deploy a self-care application with a wide range of functionality such as text messaging, blood glucose monitoring, insulin dose suggestions, educational messaging, metabolic management, pedometer counts, and reporting. Future studies are needed to develop self-care applications for a different type of diabetes with different functions of diabetes care.