Everyday technological progress enables the development of new methods of material synthesis and characterization, which encourages scientists to research and develop new and more functional coatings that meet the specific needs of different industries while being environmentally friendly. In this work, we tested the protective properties of the coatings created by the self-assembly of molecules (SAMs) of four fatty acids on the surface of copper, which were then cross-linked by ionizing gamma radiation. The coatings of non-cross-linked SAMs are not long-lasting under corrosive conditions and are removed relatively quickly from the surface. The applying gamma radiation initiates the polymerization of fatty acids, resulting in a more stable, homogeneous and long-lasting coating. In this work, the protective properties of simple and layered cross-linked SAMs of four fatty acids (Crot, C6, C18, and C22) were investigated. The protective properties were tested by electrochemical methods (Tafel extrapolation method and electrochemical impedance spectroscopy-EIS) in a solution simulating atmospheric conditions, and the coatings were additionally characterized by the contact angle method and thermogravimetric analysis. The results of the electrochemical tests showed that of the simple coatings, the C22 coatings had the best, the C18 coatings the slightly weaker and the C6 coatings the weakest protective properties. The Crot coatings offered only slightly weaker protection compared to the C22 coatings. Tests with layered coatings showed slightly weaker protective properties, and of all the tested coatings the C22 coating showed the best protective properties. The contact angle values determined by goniometry for single-layer coatings indicate the hydrophobicity of all coatings except the C6 coating, while of the layered coatings, only the C6-C18 combinations are also hydrophilic, and the other two combinations have hydrophobic properties. Thermogravimetric analysis shows that the decomposition of simple coatings takes place in one step and that the maximum temperature increases with the increase in chain length. Degradation in two stages occurs with most layered coatings, with the first drop in mass closer to the temperature determined for the shorter fatty acid, which indicates lower thermal stability compared to simple C18 and C22 coatings.