Provided are an organic coated steel having an epoxy resin layer coated on the surface of the steel product, which is formed by curing an epoxy resin composition comprising an epoxy resin and an epoxy resin curing agent as principal components and which has an oxygen permeability coefficient of 2 ml-mm/m²dayMPa or less at a temperature of 23 C. and a relative humidity of 60% RH, an organic coated steel having the above epoxy resin layer and a polymer resin layer laminated in order on the surface of a steel product and a rust preventing method for metal in which a coating layer of the above epoxy resin layer is formed on the surface of metal. The above epoxy resin layer has a high gas barrier property and a good adhesive property even under wide temperature and humidity environment, and therefore the organic coated steel and the rust preventing method for metal according to the present invention make it possible to provide a steel product having a high rust preventive and corrosion preventive effect even under severe environment and extend the life of the steel product.