Ankylosing spondylitis (AS) is a chronic inflammatory arthritis which causes potentially debilitating pain and loss of mobility. Biologics represent a highly effective treatment option in AS. Nonetheless, the choice of biologics often involves complex decision-making. A web-based medical communication aid (MCA) was designed to support information exchange and shared decision-making process between physicians and biologics naïve AS patients. This study aimed to assess the usability of the MCA prototype and the understandability of the MCA contents among rheumatologists and AS patients in South Korea. This was a cross-sectional study using a mixed-methods approach. Treating rheumatologists from major hospitals and their AS patients were recruited in this study. Participants navigated through the MCA and provided feedbacks, guided by interviewers using the think-aloud (TA) method. Participants were then asked to complete a set of surveys. The qualitative and quantitative data were analyzed to determine the usability of the MCA prototype and the understandability of the MCA contents. The MCA prototype received above average rating for usability and high rating for the understandability of its contents. Additionally, participants rated that the quality of information presented in the MCA as high. Analysis of the qualitative data highlighted three key aspects of the MCA; the usefulness of the MCA, the need to present concise and relevant content; and the importance of an intuitively designed tool. Overall, participants found the MCA to be potentially valuable in supporting the current unmet needs in clinical care and had expressed a willingness to use the MCA. The MCA had great potential in supporting shared decision-making by improving patients’ knowledge on disease and treatment options, as well as clarifying patients’ personal preferences and values in the management of AS.