Since the Second World War, the issue of regional integration has attracted attention of international relations theorists. The EconomicCooperation Organization (ECO) was established in July 1964 by the name of Regional Cooperation for Development (RCD). This organization was disbanded in 1980 subsequent to Islamic Revolution in Iran. But in 1985, all member states decided to resume their cooperation under the name of ECO. Later, collapse of the Soviet Union paved the way for expansion of ECO to 10 member States. In early years of RCD formation, Association of South East Asian Nations (ASEAN) considered today as a successful regional integration organization was established in 1967. The key question that this article poses is that given RCD (later ECO) and ASEAN were formed in relatively similar terms, why does ECO still remain at early stages of integration while ASEAN has displayed a successful pattern of integration in Asia? This paper’s main hypothesis is that although formation of these two institutions was based on “Logic of Consequence,” ASEAN has achieved deep integration and common identity by placing emphasis on “Logic of Appropriateness” while ECO has failed to create common identity among its member states.