Five and half years in office, the former Japan Prime Minister, Junichiro Koizumi, has led Japan to progress toward a wholly new direction contrast to previous Japan. Domestically, financial, fiscal and administrative reforms were Koizumi regime¡¦s primary concerns and also the core stage of Koizumi¡¦s political performance, and those reforms did somewhat improve Japan¡¦s lasting stagnant economic condition at all. Concerning of the legacy of Koizumi¡¦s foreign policy, as been regarded as a fledgling in foreign affairs at the beginning, Koizumi at last shaped the current Japan to be confident as a major power in north east Asia and more capable of facing the north Korea¡¦s threats and China¡¦s various challenges. Moreover, Koizumi made his efforts and did upgrade the Japan-U.S. military alliance de facto. In region international affairs, Koizumi also contributed to push the economic and trading integration in east Aisa. On the global level, Koizumi¡¦s Japan egaged in not only finance but also manpower contribution to the international society and eagerly did a lot to look for a leading political role in world politics than ever. Undoubtedly, the U.S. 911 attacks occurred in 2001 is the crucial agenda regarding the outcomes of Koizumi¡¦s foreign policy and surely the turning point within the context of Koizumi¡¦s foreign policy. Therefore, this paper would like to investigate¡§what things have been done in the Japan¡¦s foreign policies as Koizumi in office¡H¡¨within the following four periods,¡§Foreign Policy Review Era,¡¨¡§U.S.-first Policy Era,¡¨¡§International Consultation Era,¡¨and¡§Post-Koizumi Era.¡¨After the overall context of Koizumi¡¦s foreign policies has been well realized, this paper will discuss the profound effects and impacts cuased by those outcomes of Koizumi¡¦s foreign policy toward the three aspects of Japan domestic politics, Asia region, and the international system.