Since the 1997 Asian crisis and the commencement of the euro,renewed attention has been given to potential monetary integration in East Asia. After the 1997 crisis, many East Asian countries surrendered their pegs as they had no ability to sustain the peg exchange rate regimes. Therefore, the answers to the financial crisis could be an adoption of more flexible exchange rate regimes or a move to a hard fix such as a common currency. This study is differentiated from previous studies on OCA in East Asia in two respects. First, most previous studies focused on the evaluation with just a few criteria, which were too restrictive and potentially misleading. They also could not incorporate possible structural changes after the Asian crisis. As an alternative, this study covers more than ten OCA criteria, and extends the period that covers structural change after the Asian crisis. Second, this study proposes the Composite Index of OCA Criteria, which is the first trial in the study of OCA. Based on the Composite Index, we present a guideline for a step-by-step strategy to form a monetary union in East Asia. The results of our study suggest that relatively homogenous sub-groups — three Asian countries (Malaysia,Singapore and Hong Kong) or four countries (Malaysia, Singapore,Hong Kong and Taiwan) or six countries (Malaysia, Singapore,Hong Kong, Taiwan, Thailand, and Brunei) — could begin forming a monetary union, as a first step to form a common currency area.