This study tackles systemic functional analysis of three speeches delivered by Obama on the Iran's nuclear program 2008-2011 within the framework of critical discourse study. It investigates the implicit meanings and hidden assumptions beyond these speeches using Halliday's Systemic Functional Grammar (SFG). Context is the shared feature in Systemic Functional Grammar (SFG) which may help overcome some of the weaknesses of critical discourse analysis. Obama, the African-American president of the US, is deemed one of the most persuasive and effective speaker. His rich cultural background and various travels decorate the message. Media is the most manipulative way in the world of politics. Politicians exert their efforts to convince the audience. The results of the study show that Obama uses material, mental and relational processes to physically and cognitively gather the audience around him and to create his positive image in the minds of people.