GATT/WTO firmly establishes a global free trade regime, which is dedicated to free and freer global trade, to the benefit of all nations. However, trade liberalization poses great risk to the environment, which has been in a process of deterioration. Thus, many countries, especially developed ones, have begun to enact TREMs, with an eye to force, or induce other countries, especially developing ones, to strengthen their commitment to environmental protection. Developing countries feel they are targeted by developed ones mala fide. Thus, disputes and debates arise. This thesis is an attempted effort made to point out that TREMs reflect a deep and inevitable trade-environment conflict, to solve which the ultimate choice is environmental protection cost internalization. This is especially true for developing countries, considering GATT/WTO DSB and Appellate Body’s shifted attitude, which is given special attention in this thesis, tilting toward recognizing TREMs enacted out of genuine environmental concerns.