This article presents an argument that the formation and development of multilateral security is influenced by economic integration phase and mutual complement with bilateral alliances, through the examination of its relationship with multilateral security and economic integration and bilateral alliances in various cases. It provides the prospect of multilateral security in Northeast Asia on the basis of the analysis. In fact, economic integration has related to the development of multilateral security in Europe and Southeast Asia. There is also no theoretical and empirical evidence that bilateral alliances pre vented the establishment of multilateral security. In Northeast Asia, the formation of multilateral security will be able to start with Free Trade Agreements. FTA will be a first step for economic integration and enhance confidence building between countries through the extension of mutual exchange. The reinforcement and extension of bilateral alliances, mainly with the U.S., will be able to contribute to the formation of multilateral security in a long term. That is why it can control effectively a threat from North Korea regime and deter an excessive armaments race between China and Japan. Therefore, FTA and the strength of bilateral alliances in Northeast Asia can eventually establish the cooperation security that includes mutual confidence building and nonaggression.