The corrosion behaviour of 4-amino-3-hydroxynaphthalene-1-sulphonic acid (4A3H1S) in 0.1 M HCl on mild steel (MS) was measured by electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and potentiodynamic measurements at various concentrations. The surface morphology of the MS was examined by scanning electron microscopy (SEM) both in the absence of an inhibitor and in the presence of a 10 mM 4A3H1S-containing corrosive medium. The inhibition mechanism was determined by the potential of the zero charge (E-pzc) measurement at the solution metal interface. The adsorption of 4A3HIS on the surface of MS obeyed the isotherm of Langmuir adsorption. (C) 2014 Elsevier Ltd. All rights reserved.