This thesis analyzes the consequences of the American National Security Strategy, carried out as part of the post September 11 ‘war on terrorism’, in terms of Turkey’s security. Whether the reasons or aims of a declaration of war on terrorism are right or not, the reality is that the U.S. has made important steps with significant implications for the whole world as well as for Turkey. Terrorism, which has changed some of its features by the help of elements of globalization, hit the U.S. The U.S. perceived that fighting against terrorism could not be successful by traditional retaliation as had been done by the U.S. before September 11. This new enemy required a new plan, and therefore, a new security strategy began to be carried out. Undoubtedly, Turkey has been affected by the NSS of the U.S., due not only to her geographic position that is next to the Middle East chosen as a target place by the U.S. but also to her close relationship with the U.S. the America’s new strategy has forced Turkey to reevaluate her security priorities and threat perceptions that have been shaped by the end of Cold War. In the assessment, it is seen that the new American NSS has increased Turkey’s security anxieties.