Background: Diabetes is a global public health issue, causing burden on healthcare system and increasing risk of mortality. Mobile applications (apps) can be a promising approach to facilitate diabetes self-management. An increasingly utilized approach to facilitate engagement with mobile health (mHealth) technology is to involve potential users in the creation of the technology. Objective: The aim of this study was to use co-design for type 2 diabetes mellitus (T2DM) self-management mHealth development. Methods: Three rounds of iterative rapid prototyping panel sessions were conducted with a total of 9 T2DM participants in an Asian setting between Oct 2020 and April 2021. The participants were recruited through convenience sampling. For each round, feedback was gathered through qualitative interviews, and the feedback was used as a reference by the development team to develop and test a more refined version of the app in the next round. Transcribed semi-structured interview data was analyzed thematically using an inductive approach. Results: Participants' ages ranged from 40 to 69 years. Data saturation was reached, with no new themes emerging from the data. During the sessions, the participants expressed a variety of concerns and feedback on T2DM self-management using EMPOWER app and raised suggestions on the features of ideal T2DM self-management app. Important features include 1) reminders and notifications for medications, 2) Bluetooth integration with glucometers and blood pressure machines to minimize manual entry, 3) enlarged local food database including information on sugar content and recommendations for healthier options, 4) one touch for logging of routine medications and favorite foods, 5) export function for data sharing with physicians. Overall inputs concerned aspects such as userfriendliness of the app, customization possibilities, and educational content for the features in the mobile app. Conclusion:In this study, we explored users' opinions on a T2DM self-management mobile app using co-design approach. This study adds to the growing body of literature on co-designing behavioral mHealth interventions and can potentially guide researchers in mobile app design for other chronic conditions.