The East Sea disputes have escalated in recent years. The complexity of such dispute derivesnot only from China's aggressive actions but also from its attempt to influence to ASEAN's unity regarding the East Sea issue. As a regional cooperation mechanism containing 4 of the 10 members, there are countries with disputes over the establishment of sovereignty in Truong Sa (Spratlys), since the early 1990s, ASEAN has proved its role in settlting disputes. However, ASEAN's unity in the East Sea has been strongly influenced by China's policy. Vietnam, play a role as both an ASEAN member and a claimant, has proved its important role on the one hand. It has faced to several challenges in the efforts to resolve the disputes in accordance with in international law. By analyzing the success and limitations of ASEAN in resolving the East Sea dispute, the article clarifies Vietnam’s role and challenges in the process.