ASEAN is an intergovernmental organization within the Southeast Asia region that established in 1967 and consists of 10 member states. It’s purpose for economic growth, social progress and culture development as well as promoting peace and stability inside the region. However, due to the national interest, historic and ethnic antagonism, the ASEAN member states and its external partner keep having dispute such as border conflict, and the South China Sea conflict. Back in time, in order to avoid and solving disputes, ASEAN has established a Treaty of Amity and Cooperation (TAC) on the February 1976. The treaty includes five fundamental principles such as : (1) Mutual respect for independence, sovereignty, equality, territorial integrity, and national identity. (2) The right of every state to lead its national existence free from external interference, subversion, or coercion. (3) Noninterference in the internal affairs of one another. (4) Renunciation of the threat or the use of forces. (5) Effective cooperation among themselves. Besides the five principles, ASEAN also established TAC High Council consisting ministerial level representatives from each state to help to deal the disputes. It is considered to be a very important even though its performance is bad due to the national interest. Apart from TAC, ASEAN also has the ASEAN way, which is a conflict-avoiding system. It has two main strategic goals. First of all, bilateral disputes are not allowed to disrupt wider regional stability and functioning in ASEAN. Second, do not let bilateral issues between ASEAN states and Non-ASEAN states affect the intra-ASEAN-relation (Weatherbee, 2009}. Although ASEAN is claimed to be one of the most important regional intergovernmental organization in Asia, its ability to dealing with interstate conflict is still weak. This paper is going to discussed why ASEAN is ineffective beginning with the weakness of the ASEAN mechanisms, principles and concluded with recommendations on how ASEAN could improve its way of dealing with conflicts.