This article analyzes the changing role of the United Nations in the post-Cold War era. After the end of the Cold War, many internal conflicts broke out in different parts of the world. There was a dramatic demand for the UN peacekeeping operations. Thus, the UN started to challenge traditional norms of international politics, such as state sovereignty, non-intervention into domestic affairs, and non-use of force in peacekeeping operations, and itself as an international organization. Within this context, this paper vvill examine the UN peacekeeping operations in the post-Cold War era; former Secretary General Boutros Ghali's "An Agenda for Peace"; case studies of Bosnia, Somalia, Rvvanda, Haiti and Cambodia; blurring distinction betvveen peacekeeping and peace enforcement; and humanitarian intervention of the UN. The article also seeks to analyze structural reform proposals for the UN to respond the challenges it faces today. Current issues of the Security Council reform proposals and fınancing the UN vvill be discussed.