BackgroundMobile phones can be an ideal platform to engage adolescents to maintain, improve, and promote self-care. Therefore, the current study aims to design and evaluate the usability of a mobile application for self-care in adolescents with a user-centered approach.MethodsThe current applied developmental study was done in four steps. The first step, polling and examining opinions was conducted through in-depth semi-structured interviews, with the aim of user-centered mobile application design with the involvement of 30 participants. The second step, extracting and compiling the educational content related to the main themes of the self-care app, was obtained from national and international guidelines and instructions, including the World Health Organization, the Center for Disease Control and Prevention, the Ministry of Health and Medical Education, etc. In the third step, the initial version of the mobile application was developed. In the fourth step, app usability was evaluated by 30 participants from the target group, 2 weeks after using the app, using the MAUQ questionnaire.ResultsIn the first step, 789 codes, 12 sub-categories, and 3 categories were extracted. These codes were used in the design of the mobile application. In the second step, educational information was prepared and arranged in 5 sections (physical activity, nutrition, personal hygiene, risky behaviors and safety and events) in the form of text, images and short videos. In the third step, the mobile application was designed based on step 1 and 2. This application operates in online mode and under the Android operating system. the initial version of the mobile application was developed using JavaScript and Typescript programming languages in a Visual Studio Code environment. In the fourth step, the participants the overall level of usability of the application as very good with an average of 6.28 ± 0.55. The highest average score was given to the user interface and satisfaction with an average score of 6.43 ± 0.58.ConclusionsThe "My-Care" app is a collaboratively designed smartphone app for adolescents that targets 5 dimensions of physical self-care. This app has the potential to teach, assess, and promote self-care among adolescents.