The optimum conditions for the anti-corrosion behavior of the octadecylamine (ODA)-treated iron samples in electrolytes containing chloride, sulfate and carbonates ions were established using electrochemical impedance spectroscopy. The best protective ODA film was formed on the surface after the iron samples were treated in steam at 220 degrees C in an autoclave for 1 h, using a solution ODA concentration of 25 mg/L. The photoelectrochemical results revealed that ODA modified the physical structure of the iron oxide layer. From the Auger electron spectroscopic analysis, it is believed that the surface layers of the ODA-treated samples consisted of one of the following structures: at ODA concentrations < 20 mg/L: iron/iron oxide/mixed ODA-iron oxides; at ODA concentrations greater than or equal to 20 mg/L: iron/iron oxide/mixed ODA-iron oxides/ODA.