The writer analysed the presupposition in Barack Obama’s speeches on his first and second inaugural addresses, the writer comes to conclusion mentioned as the following. In this study the writer found that there are five types of presupposition. They were Existential presupposition (53.12%), Factive presupposition (15.17%), Lexical presupposition (24.55%), Structural presupposition (6.69%), and non-factive presupposition (0.44%). The most dominant presupposition used in Barack Obama’s speeches in his first and second inaugural addresses was Existential presupposition. It was because the speeches contained more definite descriptive, real facts and real information to stimulate the audience’ attention and to emphasize his ideas and promises.