Mobile Application is proven to be able to help encouraging the effectiveness of using public transportation, including the MRT Jakarta transportation. However, based on preliminary studies, it was found that there are still many users who experience difficulties when using the MRT Jakarta mobile application. For this reason, the application's user interface is needed to be redesigned to make it easier for users to use it. This research mainly uses the Usability Testing method. In conducting Usability Testing, Performance Measurement is used to measure the application usability quantitatively, Retrospective Think Aloud, to find out the responses or suggestions from users, and USE Questionnaire (Usefulness, Satisfaction, and Ease of Use Questionnaire) to find out the general subjective assessment from users about the MRT Jakarta mobile application. This study provides new improved design recommendation for the MRT Jakarta Mobile Application, that refers to Material Design and 10 Usability Heuristics for User Interface Design by Nielsen. The results of this study indicate that the redesigned user interface is proven to have a better usability level than the previous design.