This article explores the constitutional roots of the treaty-making power of Iraqi and the US constitutions. Undoubtedly, with regard to international relations including making treaties, the federal government is on a better foot to represent the whole people of the state. The scope of the treaty making power is not controversial in unitary states, because there is only one centralized government practicing sovereignty in making treaties. In federal states, however, there is more than one sovereign body within the country, and in subsequence the federal government should always avoid encroaching on state reserved powers. The threat of unlimited treaty making power has strongly appeared as a parallel to the dramatic changes of contemporary international relations, and this relatively pushed law scholars and judges to reconsider the treaty making power. These judicial and jurisprudential disagreements about the treaty making power and its limits are the core subject of this paper.