The inhibition of corrosion of pure iron in 0.5 M H2SO4 by ethanolamines such as mono-, di- and triethanolamines has been investigated by dc polarization and ac impedance techniques. The results showed that a strong dependence of inhibitor performance with concentration in addition to the structural effects of amine molecules. From impedance data it is found that the corrosion of iron is controlled by charge transfer process at all concentrations of inhibitors. All the three inhibitors are found to hinder the formation of passive film on iron. (c) 2004 Elsevier B.V. All rights reserved.