A study has been made of the adsorption and corrosion inhibition of iron by triethanolamine salts of 18C unsaturated fatty acids in 0.5 M deaerated H 2SO 4 solution. The adsorption was considered in terms of the competitive coadsorption of acid molecules and amine cations, being the main species in this solution. From measurements of differential double layer capacitance and dissolution kinetic of iron, the preferential adsorption of fatty acids over amine has been found. The orientation of acids appeared decisive for the formation of inhibitory effective adsorbates. Such adsorbates were originated by vertically oriented oleic acid molecules. Less effective were the layers based on salts of acids possessing a greater number of Π bonds. The double, horizontal and vertical orientation was found for these acids. The main role of amine was the cross-linkage of acid chains adsorbed on the iron surface.