This article aims to explain about the role as wartime leader of President Syngman Rhee during the Korean War(1950~1953). The Korean War was the most difficult and potentially the most disastrous of the early Cold War period, a conflict which directly involved one of super powers in open war with the most populous state in the world. The other super power was only indirectly involved but there was always the possibility that it might intervene; a third world war could erupt. This study has tried answer the following key questions:(1)How did President Syngman Rhee act the initial stage and after of the North Korea's surprise attack against the Republic of Korea (ROK)? (2)What was war policy and objective of President Syngman Rhee? (3)When and Why did President Syngman Rhee try to penetrate 38th parallel? (4) Why did President Syngman Rhee involve the United Statesinto the Korean War? (5)What was role of President Syngman Rhee as a wartime leader during the Korean War? (6)What did President Syngman Rhee obtain from the United States after the Armistice? In seeking answers to the above questions this paper used the State Department Foreign Relations of the United States, Documents and Files of the Korea Government, the Korean War History of Ministry of National Defense of the ROK, and the Memoirs of those officers and generals who played a nactive part in policy-making were consulted. In conclusion, President Syngman Rhee achieved an enforcement of the Korean armed forces and the ROK-US alliance relations through 'Mutual Defense Treaty between the Republic of Korea and the United States of America'. In this concept, he was agreat patriot, national leader, wartime leader like Winston Churchill or Franklin Roosevelt, and international political scholar and leader.