Electropolymerized polyaniline (PANI) is able to protect iron against corrosion for several weeks, even in the absence of inorganic conversion layers or topcoats. During the PANI deposition process, iron is passivated and the subsequent protection is dependent on the nature of the passive layer, which is stabilized by PANI. The composition of the solution in which PANI is polymerized can modify the passive layer as well as the polymer and Raman and optical spectroscopies are used to characterize the properties of PANI potentiostatically electrodeposited from phosphoric/metanilic solution (electrodeposition solution). The presence of phosphoric acid strengthens the passive layer, while metanilic acid is inserted in the polymer backbone to form a copolymer which presents higher protective properties.