Introduction: Admission and medical record system (AMRS) is one of the most important subsystems of hospital information system, which is used by many users in admission, discharge, and health information management. Interface usability problems can reduce user speed, precision, and efficiency in user-system interaction. This study aimed to identify the usability problems of AMRS in a hospital information system. Method: In this descriptive cross-sectional study, five health information technology experts evaluated AMRS in a hospital information system using heuristic evaluation. Then, the system usability problems were categorized according to Nielsen's 10 usability principles and their severity were determined. Results: Totally, 62 unique usability problems were detected. The most frequent problems were related to "consistency and standards" (n=9) and ''recognition rather than recall" (n=9), and the least frequent ones was related to "flexibility and efficiency of use" (n=1). 59. 7% of the identified problems were categorized as big and severe problems. The highest average severity of problems belonged to "system’ s visibility" and "aesthetic and minimalist design", and the least average severity belonged to "error prevention". Conclusion: Using heuristic evaluation, a large number of usability problems in AMRS were identified. According to experts' opinions, most of the HIS interface problems were big and severe, and they need to be modified by designers and developers of these systems.