Two ethoxylated nonionic surfactants (L400 and L600) based on Schiff base are prepared from polyoxyethylene, glyoxalic acid, and phenylenediamine. They are evaluated electrochemically as carbon steel corrosion inhibitors in 1 M HCl by electrochemical impedance spectroscopy (EIS) and Tafel techniques and complemented with microscopic analysis methods. The obtained Tafel data indicate the mixed-type behavior of the inhibitor used. The inhibition efficiency touches the peak at 1 × 10 –4 M, exhibiting 92 and 94% for L400 and L600, respectively. The presence of the tested inhibitors decreases corrosion current density ( i corr ) and double-layer capacitance ( C dl ) due to the formation of a protective adsorption layer in place of the already adsorbed water and aggressive Cl – ions. Both L400 and L600 adsorption modes follow Langmuir adsorption isotherm. The density functional theory (DFT) calculated indices (Δ E gap and E HOMO ) indicate the superiority of L600 over the L400 counterpart as a reactive compound. Adsorption of L600 and L400 over the Fe(1 1 0) in simulated acidic medium is investigated by Monte Carlo (MC) simulation to verify their inhibition performance and are matched with adsorption free energy Δ G ads calculated values. Both experimental and theoretical data are in agreement.