Market structure is one of the most important characteristics of every industry. Although there is different indices such as concentration, economies of scale, entry of firms, product differentiation, etc. for the evaluation of market structure, most of the studies in the subject have used only one of these indices (usually concentration). In this study, by application of fuzzy inference approach, a comprehensive index is constructed by combination of concentration, economies of scale and the number of entering firms’ indices. The constructed comprehensive index is used for the evaluation of market structure of Iranian 4-digit ISIC manufacturing industries in 2007. The results indicate that in most of the industrial sub-sections, the calculated comprehensive index is low, which is mostly due to low values of economies of scale in such industries. Also, based on the results of calculated comprehensive index, the industries of manufacture of bricks and manufacture of jewellery and related articles are the most competitive and the most monopolistic industries, respectively.