The objective of this research is to design and develop a Web-Based Hospital Information System for the Outpatient Department (Web-Based HIS-OPD), specifically focusing on five core clinical service modules: Diagnosis, Medication Ordering, Medical Certificate Issuance, Laboratory Ordering, and Radiology Ordering. The content validity of the evaluation instruments was verified by 3 experts. The system was evaluated by a purposive sample of 20 outpatient clinical staff, including physicians, nurses, and officers. The results demonstrated that the system achieved 100% functional accuracy across 220 test cases. Furthermore, the user evaluation indicated a high level of overall satisfaction and usability (M = 3.93, S.D. = 0.36). Specifically, the system exhibited high effectiveness in reducing data redundancy (M = 3.92, S.D. = 0.61), enhanced operational speed compared to the legacy system (M = 3.88, S.D. = 0.67), and a high level of system usability (M = 4.00, S.D. = 0.49). These findings suggest that the developed system significantly reduces clinical data redundancy and practically enhances the efficiency of data accessibility.