This thesis is written by containing an explanation related to the foreign policy of United States under Barack Obama towards Iran‘s nuclear program. Obama‘s foreign policy by viewing from the advantages and disadvantages of the outcome. Theoretical frameworks used by this thesis to analyze the problem are Foreign Policy Analysis, Rational Choice theory and model of Rational Actor in analyzing US foreign policy towards Iran‘s nuclear program. Under two different leaders, President George W. Bush and, then, Barack Obama, the result of this research shows that in policy related to Iran‘s nuclear program made by Bush and Obama, there are differences. The differences laid down on the decision which is preferred to the options taken by the leader to direct his foreign policy. In this case, Bush intends to confrontation approach by using ‗hard power identical‘ threat—such as military force, while Obama put more efforts in diplomacy or soft power approach. In this research, it is proven that the differences caused by individual factor and leadership characteristics as rational actors. The findings of this research that are Obama wants to protect the achievement of political advantages, defends security in Middle East and keeps US economic advantages and its allies in hand.