Structural changes in international relations since the end of the Cold War have brought the globe in a transitional phase with new characteristics. The new era and conditions have made regional cooperation on different zones of the globe more important, so as success of a country in playing effective and constructive role in its peripheral area can be an introduction for its successful entrance on global arena. At the same time, it should be considered that success in regional policies is not only a function of the possibilities of each country of a region but also depends on participation of all regional countries in the process of regionalism. Regionalism means to use the potentials of a region towards integration which becomes possible in the framework of a regional system. Regional system represents the mechanism of interactions in a region and the process of influence of internal and peripheral variables on regionalism. Since ECO is the most important and comprehensive regional organization for Iran as its member, we are to examine in this article the possibility of regionalism in the framework of ECO through giving theoretical standards. So we will take into consideration effective variables - geographical, political, security, socio-cultural, and intervening systemic - in a comparative manner for ECO.