This article examines the conception of ‘East Asian Community’ during the Hatoyama administration and the foreign policy of the Hatoyama administration with focus on the policy toward Asia, especially South Korea. The Democratic Party of Japan(the DPJ) won by getting 308 seats at the Lower House election in Japan held on August 30, 2009. The change of power from the Liberal Democratic Party of Japan (the LDP) to the DPJ in the Diet was an epoch making event of the Japanese political history after World War Ⅱ. The DPJ proposed the conception of ‘East Asian Community’ through the manifesto at the general election in 2009. The Conception of ‘East Asian Community’ was useful to clear the new foreign policy line is different from the former administration. On the other hand, PM Yukio Hatoyama’s proposition of ‘East Asian Community’ caused the Obama administration’s concern over the Japan‐U.S. relations. The Hatoyama administration had showed intra‐regional cooperative mechanisms in such areas as trade, finance, energy, the environment, disaster relief, and measures to control infectious diseases, as their policy objectives based on the conception of ‘East Asian Community.’ Therefore, the conception of ‘East Asian Community’ doesn’t include the cooperation on the military security policy in the Asia‐pacific region. The Hatoyama administration had tried to make and maintain the stable relationship with South Korea. On 9 October 2009, PM Hatoyama visited Seoul and had the summit talk with President Lee Myung‐Bak. In the summit talk PM Hatoyama and President Lee discussed the North Korean issue. President Lee explained the design of ‘grand bargain’ which is to settle the North Korean nuclear problem. They also confirmed the cooperation between Japan and South Korea to advance the conception of ‘East Asian Community.’On the other side, the Japan‐U.S. relations was somewhat drifting because of the U.S. base problem in Okinawa. Actually, the flexible balance between the foreign policy toward Asia and the foreign policy toward the U.S. has been the key subject on the foreign policy of Japan, for the long time. Japan had suggested many conceptions of the foreign policy in the past. For example, ‘An Arc of Freedom and Prosperity’(PM Taro ASO), ‘The Synergy between the Japan‐U.S. alliance and Japanese Diplomacy toward Asia’(PM Yasuo FUKUDA), and so on. These conceptions stemmed from the Japan’s basic objectives of the foreign policy, (ⅰ) the maintenance of the Japan‐U.S. alliance, (ⅱ) the quest for autonomy, (ⅲ)the development of the relations of mutual trust with Asian countries. Interestingly, PM Hatoyama’s conception of ‘East Asian Community’ also originated from these three basic objectives. Although the Cold War ended and the ruling party changed in 2009, these three points remain the Japan’s salient issues of the foreign policy as before. Perhaps, in the Hatoyama administration’s case, the quest for autonomy was of priority. Anyhow, even though the ruling party changed, Japan’s basic objectives of the foreign policy don’t change dramatically for the time being. In such a situation, the important phase of the Japanese Foreign Policy would be the Japan‐South Korean relationship. Because Japan and South Korea could share the common security objectives in East Asia. In addition to that, Japan and South Korea have the geographical advantage to the economic, cultural, and educational exchange between the two nations. It must be pointed out that the Japan‐South Korean relations have already become the highly important theme of the Japanese foreign policy.