A series of substituted benzylidene Schiff bases (2-4) were tested for their corrosion inhibition efficiency on mild steel in 1 M HCl at 25 degrees C using electrochemical impedance spectroscopy, polarization and linear polarization resistance measurements. Experimental results demonstrated that the corrosion inhibition efficiency of the Schiff bases is more potent than their parent amine (1). XPS analysis proves the entire molecule of 3 ligand chemisorbed through a covalent bond (pi to pi) interaction as found in C=C in the benzene ring and C=N. The correlation between the corrosion inhibition efficiency and physicochemical and electronic properties of inhibitors (1-4) was investigated by using density functional theory method. Theoretical results clearly showed that the corrosion inhibition efficiency mainly depends on the frontier orbitals parameters (e.g., ionization potential, and electronic affinity).