Background: Mobile health (mHealth) applications have become integral in medical education and information access, yet effectiveness varies, and barriers to engagement persist. OBJECTIVE: This study aimed to assess the usability and effectiveness of the mHealth application entitled Hypertension Now in increasing knowledge and guideline adherence among residents. Methods: A before-and-after educational intervention study was conducted among residents of the Department of Family and Community Medicine (DFCM), Philippines General Hospital from January to August 2023. The intervention was a newly developed medical reference app for managing hypertension based on the latest local and international hypertension guidelines. Usability, knowledge score, and adherence rate were measured using a questionnaire, pre- and post-intervention examinations, and medical chart audits. Results: All 32 DFCM residents participated in the study. The app was rated high on ease of use and usefulness for practice by the residents. It was also rated high on interface and overall satisfaction. It significantly increased the knowledge scores of the residents by 1.6 points (p=0.001). The proportion of those who passed the exam significantly increased post-intervention (37.5% vs. 59.4%, p=0.035). Moreover, the app increased the adherence of the residents to proper physical examination (82% vs. 91%, p=0.024), diagnosis (80% vs. 90%, p=0.012), and pharmacologic treatment (53% vs. 83%, p=0.001). There was no increase in adherence to proper risk assessment (83% vs. 78%, p=0.371), laboratory examination (35% vs. 40%, p=0.329), and non-pharmacologic treatment (77% vs. 81%, p=0.470). Conclusion: The mHealth app for hypertension management was usable and effective in increasing the knowledge of family and community medicine residents in managing hypertension. While the app increased guideline adherence to physical examinations, diagnostics, and pharmacological treatments for hypertension, it did not increase adherence to risk assessment, laboratory examination, and non-pharmacologic treatment.