The results of a systematic electrochemical and ellipsometric study of polyaniline films grown in aqueous solutions under several potentiodynamic conditions on platinum electrodes are described. The aim of the work was to characterize the mechanism of growth and the structural properties of the polymer in several stages of growth in sulfate and chloride acid solutions. It was observed that under all conditions, the electrochemical cycling growth of the polyaniline film starts with a nucleation process, during which a hydrous structure is formed. After the nucleation step, the continuation of growth proceeds with an increase of the polymer chain length and an increase in the number of sites in the oxidized state. Finally, after a critical thickness, there is a significant change in the growth mechanism, and the formation of a completely open structure takes place. It was also observed that the degree of the optical and oxi-reduction activities and thus the structure of the films are functions of the upper limit potential and the nature of the electrolyte employed in the synthesis.