When the mechanical cleaning of metallic surfaces is not possible, some chemical treatments are an important possibility. The benefit of using acidified aqueous suspensions of tannins in this field has been recognized for more than thirty years. However, little is known about the action of these substances on rusted surfaces. Thus, the chemical reaction of tannins with soluble and precipitated ferric species was studied. The influence of the phosphate anion was also considered. At the same time, cleaned and oxidized steel surfaces, treated with tannin suspensions were analyzed by microscopy and scanning electrón microscopy (SEM) to observe the surface film morphology. Four tannins were selected to carry out this investigation: quebracho, sulphitated quebracho, mimosa and chestnut. The experimental results show that each tannin reacts with soluble and precipitated ferric species in a different way. This reaction depends on the pH of the solution. The tannate film formed on the steel surfaces had a píate morphology which also depended on the tannin. The presence of phosphoric acid contributed to the tannate film building.