The main goal of this research is to identify the effective factors on tax evasion by fuzzy DEMATEL-method in Iran. At the present time tax evasion is one of the economic problems in developing countries. Our country has had in this problem for several decades. In this paper, we attempted to determine effective factors in tax evasion, and the relational structure of these factors is examined by fuzzy DEMATEL-method, and meanwhile to recognize their interaction, the hierarchy of the influence of these factors should be known, too. research results showed that among the effective factors, lack of law-makers, of dominance interference institutions which are not charge and the vast exemptions have the highest impact on tax evasion
