As the world’s population is aging, research on older adults and their use of IT is becoming more important. Usability issues were found one of the main problems hindering older adults from using IT, including mobile health application. This study aims to understand older adults’ behavior and to identify barriers and enablers for using a mobile health application, called Raksa. Two theories, namely Usability and Accessibility were adopted as a conceptual framework. A think-aloud protocol, a system usability scale (SUS), and in-depth interviews were utilized. ISO 9241-11 guide was used for identifying usability performance level of Raksa application based on think-aloud approach. Task incompletion rate, error rate and time on task were calculated to assess effectiveness and efficiency. Interviews were conducted for validating reason of use and comment on the application design, using Nielsen’s 5 quality components namely, Learnability, Efficiency, Memorability, Error and Satisfaction. The results showed that the task to find a medical specialist for a consultation was deemed the most difficult by the participants as it has the lowest task completed rates and the longest times on task. The task to create account and register had the most errors. The average satisfaction (SUS score) was 31.50, indicating poor system usability. Demographic data showed males were more successful in task completion. Educational level were related to task performance, and older adults with more experienced in information technology or social media achieved higher performance rate. This research identified usability problems and barriers that may affect usability in older adults, including visual design, poor interaction and navigation, user interface difficulty to understanding. Recommendations for design modifications were offered.