From 1970 the NPT Review conferences have been held each five years. Up to now, eight conferences are held in the United Nations headquarters in New York. These conferences aimed to find an international solution to deter proliferation of nuclear weapons, to ensure full compliance of the member states with the NPT regulations and to give functional ways for addressing challenges ahead. The US approach, as an influential member of the NPT, toward this issue is of great importance. The aim of the present article is to make a comparison between the US views and positions in the Review Conference of 2005 and the Review Conference of 2010 in light of US nuclear strategy in Bush and Obama administrations. The US stances towards Iran in these conferences will also be analyzed.