Achieving sustainable peace and establishing effective mechanisms for it are fundamental issues of international law that have received intense attention, especially after the formation of the United Nations and the Security Council. The Security Council, as the main institution responsible for maintaining and developing international peace and security, requires legitimacy in its decisions. However, some factors, such as the veto right and the dominance of the permanent members of the Security Council over its decisions, have reduced the legitimacy of this institution. This has led to some decisions of the Security Council, especially in times of global crises, facing serious criticism. One way to strengthen the legitimacy of the Security Council is to eliminate the unfair veto right and more equitably distribute influence among member states, especially non-permanent members. The present study, using a descriptive-analytical method, examines the challenges to the legitimacy of Security Council decisions and the impact of various factors on them, and offers suggestions for improving this legitimacy in order to achieve sustainable international peace and security.