Income tax does have allocative and distributive roles in economy. So, one of the key roles of income tax is distributive. The major principle of this type of tax is "justice principle". This paper uses a modified version of the Engel, Galetovic and Raddatz model to examine the effects of salary tax on the Income distribution in Iran.The findings of the paper confirm that the optimal tax rates in Iran are 25.18, 28.28, 12.5, 12.5, 12.5 percent, respectively, over the period of the third five-year development plan. Comparing the actual tax rates with the optimal ones, it is observed that there exists a significant gap between potential and actual tax rates in the country.