Many efforts have been made to describe and control the formation of polypyrrole layers on iron. The corrosion protection performance of these layers has been greatly improved through the variation of their bulk properties such as the size of the counter-ions or the inclusion of metallic oxide nanoparticles. In this work, the properties of the iron/polypyrrole interface have been varied through a set of iron surface pre-treatments. Surface analysis techniques allowed to monitor this variation, which proves to have a strong influence on the corrosion protection performance of polypyrrole-coated iron. A clear correlation could then be established with the electrochemical impedance spectroscopy (EIS) data by modelling the system with an equivalent circuit. The properties of the iron/polypyrrole interface were quantified and this quantification was confirmed experimentally by the use of a mercury cell.