The United States has played the most important role in maintaining security and stability in East Asia since the end of the Cold War. As some scholars have argued, the current international order has been built not on the principle of balance of power but on American hegemony. The purpose of this paper is to dwell on U.S. security strategy in East Asia after the September 11th attacks and on how this new strategy has changed the security environment in this region. The paper also wants to evaluate whether the Bush administration's security strategy is favorable or unfavorable to security in East Asia and what policy the United States should take to maintain a strong role of leadership and stability in East Asia.