The inhibition effects of 11-cyano undecanoic acid phenylamide derivatives against corrosion are studied by means of density functional approach B3LYP/6-311G(d,p) calculations. The efficiencies of corrosion inhibitors and the molecular structure relate to some parameters, such as E (HOMO), E (LUMO), the energy gap between E (LUMO) and E (HOMO) (Delta E = E (LUMO) - E (HOMO)), dipole moments (mu), and other parameters, including electronegativity (chi), global hardness (eta), softness (rho), chemical potential (mu(c)) and the fraction of electrons transferred from the inhibitor molecule to metallic atom (Delta N). The computed quantum chemical properties indicate good correlation with experimental corrosion inhibition efficiencies of 11-cyano undecanoic acid phenylamide derivatives. A good correlation between the substituent type and inhibition efficiency of inhibitors through the application of Hammett relationship is obtained. The linear correlation is also found between the Hammett parameters and calculated molecular orbital energies.