Objectives : The formation and expansion of NGOs inside and among different countries has been the center of pondering and consideration of thinkers, with the aim of support and protection the rights of human being and nature, real and organized participation of people in determining their own destiny for improving the social life conditions. This article evaluates the theoretical functions of NGOs with emphasis on NGOs in Iran and an specific attention on environmental NGOs . Method: This is a descriptive study and its data has been gathered by documents and interview with 50 active members of the environmental NGOs. The data has been coded in order to analyze the main social, economic, political and legal problems facing these organizations. Finding: The findings show the growth of NGOs in Iran. Although this growth in quantitative regard is admirable, but the necessary data for the evaluation of their operation and function is not available. Concentration on the functions of the environmental NGOs indicates the structural and organizational problems in social, economic, political and legal dimensions of these organizations. Ambiguity in laws and regulations of these organizations, weakness in managerial skills controling them, government and politically interest groups interference in their activities are among the most important problems of these organizations. Results: Along with the theoretical grounds governing the behavior of NGOs in the world, this article tried to evaluate the position and function of NGOs in Iran. The recognition of structural and organizational limitations governing the environmental NGOs in Iran as an example of these kinds of studies and the manner of expert removal of these limitations can lead to positive functioning of these NGOs and provide suitable conditions in the social system in order to support these NGOs in general.