This paper analyzes the feasibility of a monetary union in Southeast Asia. Based on one of the monetary unions' optimality criteria of symmetry of shocks, a study of ecomic cycles is carried out using a VARs approach, in order to assess the degree of this symmetry of shocks between three Asian countries (Korea South, Singapore, Thailand). The results show that, despite the similar similarities between these different economies, especially in the face of global shocks such as invitations to the world price of oil, they are different in their responses to domestic shocks and in the way they conduct their monetary policy. These differences are important enough for a monetary union to be discouraged between them. Regarding the adoption of an existing currency (in the case of the US dollar here), only Singapore seems to have a business cycle quite similar to that of the US to take advantage of such a policy.