The UN is the most important international organization whose activities vary from international security issues and world peace to fighting against AIDS, promoting education, human rights and other issues around the world. The UN consists of six principle organs, one of which is the Security Council. UN action, however, during the last six decades, particularly in the Cold War era, indicates that the Council is the most important and powerful organ. Yet, the problem is that due to the present combination of the members of the Security Council it reflects the "balance of power" system of the post-Second World War era, which does not fit in today's world situation and international relations. Therefore, one can refer to the need for reform in this Council to enable it to respond to the emerging demands. This paper aims to study the need for structural reform in the UN Security Council. It tries to answer the question: What kinds of reform must be made in the Council? The main argument of the paper is that with a change in the structure of the international system after the Cold War, the emergence of the new world powers and, particularly, the increase of the UN members, structural reform in the Security Council is crucial. To maximize its legitimacy and influence the Council should be a reflection of the new world order.