Knowledge-sharing is considered one of the fundamental processes in knowledge management and has a vital role in improving performance in different public and private sectors. It helped to enhance learning and innovation and improved the decision-making process in academic libraries in Oman. Moreover, the Group Decision Support System (GDSS) is considered a widely used library system in libraries. Therefore, this study aimed to identify the impact of knowledge sharing using the Group Decision Support System (GDSS) on improving the decision-making process in Omani academic libraries (public and private). The study relied on a mixed approach that combines quantitative and qualitative methods to examine the research objective comprehensively. One hundred and ninety-three questionnaires were collected from Omani academic librarians. Then, regression analysis is used to test the study hypothesis. In addition, the researcher conducted eight interviews to provide a qualitative interpretation of the quantitative findings, ensuring a robust and integrated analysis. The study findings confirm the positive correlation between knowledge sharing and its factors: information technology use, collaboration, and management support. Information technology use and collaboration influenced knowledge sharing, while management support was insignificant. The study's findings also showed the positive and significant impact of knowledge sharing and the Group Decision Support System (GDSS) in improving the decision-making process. Finally, the findings suggest a framework for future studies that could add factors to this model, such as trust as a key individual factor, and create new measurement models to enhance knowledge sharing.