Chemical surface modification of iron by I-phosphono-alkane derivatives in aqueous solution has been studied by EIS. The phosphonate layer formation in time was followed by the change of polarization resistance and interfacial capacitance values of iron substrate. Significant corrosion protection was observed due to the spontaneous adsorption layer formation. The protective layer is supposed to have a continuous and dense structure. The inhibition mechanism is anodic type, hindering the active iron dissolution to a large extent. The kinetics of phosphonate layer formation is a complex process. Beside the fast adsorption of molecules on bare iron surface, ordering in the layer structure is taking place during long immersion time. The layer formation process of alkane-diphosphonates and monophosphonates were compared.