Many observers believe that the United Nations has failed to achieve its most important goal which is maintaining international peace and security. The present article, assuming that neo-idealist approach is appropriate for studying the causes of the crisis in the UN functionality, aims to assess the United Nations performance. Based on this approach, elements such as developments in the structure of international relations, the notion of security, global political players, inability of the UN to adapt itself with these developments, undemocratic structure of the UN Security Council, and the US unilateralism are identified as root causes behind functional crisis of the UN. It is also suggested that a fully-reformed UN structure striped of ‘veto power’ could be a functional body to cherish and sustain global peace and security.