The anti- corrosion performance of iron is greatly improved after octadecylamine (ODA) treatment. It is assumed from AES that the structure of surface layer of samples treated with ODA is as follows: Lower ODA concentration: iron | iron oxide | ODA layer with iron oxide Higher ODA concentration: iron | iron oxide | ODA layer with iron oxide | pure ODA layer It is shown from infrared specular reflection that the surface layer of iron treated with higher ODA concentration reflects ν (CH) absorption peak corresponding to pure ODA layer. Every ν (CH) absorption peak shows opposite absorption phenomenon because of reflection from the iron oxide, which is under the pure ODA layer.Photoelectrochemical study exhibits that ODA treatment leads to the changes in physical structure of iron oxide layer. ODA treatment was successfully applied to lay- up protection in power plant.