This study attempts to examine transitional history for understanding the relationship between regionalism and hegemonic competition of core states in East Asia. Globalization has provided opportunities for a new economy with growing states in East Asia since the 1970s. The emergence of new regionalism in East Asia has risen with the competition of hegemony between core states from the end of the 1980s. The economic liberal strategy of APEC that was initiated by the US and Australia contrasts the EAEC that supports developmental strategy in East Asian developing states. Since the Asian financial crisis, the emergence of China, based on structural market power and independent political sovereignty, has reshaped the Asian regionalism. In addition, the APT has brought competition between China and Japan. This study argues that regional organizations in East Asia have been instruments to intensify regional hegemony in strong states and to maintain state sovereignty in weak states.