East Asian regionalism substantially intensified after the 1997-8 Asian Financial Crisis (AFC), which was a significant case and an increasingly emerging issue of new regionalism after the Cold War ended in the early 1990s. In contrast with business-led regionalization, government-led regionalism was the key way leading to East Asian economic integration, of which bilateral governmental economic cooperation between China and ASEAN was the substance. The thesis explores China’s shifting role in economic cooperation with ASEAN before and after its WTO accession in 2001 within a theoretical framework of complex interdependence. In the bilateral interdependent economic relations, China became a mutual complementary partner of ASEAN from a natural competitor; and became a foreign direct investment (FDI) source of ASEAN from a net recipient after the WTO accession. This laid a sound basis for China to be well placed as the leader in East Asian economic integration. The thesis investigates the motives that prompted China to shift its attitude towards economic cooperation with ASEAN (clearly illustrated by China’s initiative of the China-ASEAN Free Trade Area (CAFTA) proposal in 2001) from a Chinese perspective. China’s grand strategy, which highlighted the neighbours’ stability and prosperity in political sense and exploration of regional markets in neighbour countries in economic sense, was the radical motives. In addition, Beijing desired to diminish the two domestic problems: the disparity between East and West China and the gap between the urban and rural areas by enhancing economic cooperation with ASEAN. This, as the key motive, induced China’s shifting attitude towards economic cooperation with ASEAN and towards economic integration in East Asia. This thesis contributed to the second wave of regionalism studies after the 1997-8 AFC by examining the implications of China’s domestic politics on regionalism in East Asian case from a Chinese inward-looking perspective.