The Trans-Pacific Partnership (TPP) is a proposed regional free trade agreement across the Pacific Ocean, dominated by developed countries, especially the United States. Several members of the Association of Southeast Asian Nations (ASEAN) are currently participating in the negotiations. This paper seeks to examine the implications of the proposed agreement towards the cohesion of ASEAN. Based upon the existing literature and empirical considerations, first, the paper finds that the TPP is likely lead to further weakening of the organization since stronger trading relationships might lead to a political-military alliance, namely between ASEAN members in the TPP with the US. Second, the disparity of fortunes caused by the inclusion of only some ASEAN members inside the TPP might cause further weakening of ASEAN cohesion.