One of the most important dimention of the industrial structure is the concentration. In order to determine concentration in Iranian industries from 2000 to 2005, the 5-firm concentration ratio is used in terms of sale value, production, value added and employment variables. The results indicate high correlation among concentration ratios in terms of sale, employment, value added and production value: the correlation between sale concentration ratio and that of production has been about 0.9983, sale and value added 0.9611, and between production and value added about 0.9617. Concerning the results, and avalilability of the data, application of the value added concentration ratio is preferred. Despite reduction in industrial concentration, the concentration in most of industries in Iran has been high and display monopolistic structure. Although this is the case in terms of value added concentration ratio, using employment CR reflect that most industries are run in a state of competition. In most of the years durig research period, manufacture of tobacco products, recycling, manufacture of coke, refined petroleum products and nuclear fuel, and manufacture of motor vehicles, trailers and semi-trailers have had concentration ratio of over 70 percent. This has been the case while Texciles industry has been less concentrated industry in terms of all four variables (sale, production, employment and value added).
JEL Classification: C46, L11