Inhibiting effect of 4,6-diamino-2-pyrimidinethiol (4D2P) on mild steel corrosion (MS) in 0.1 M HCl solution was investigated by linear polarization resistance, electrochemical impedance spectroscopy and potentiodynamic measurements in the presence of different concentrations of 4D2P ranging from 10.0 mM to 0.5 mM. The effect of 4D2P on the MS corrosion was also studied by scanning electron microscopy and quantum chemical calculations. The adsorption of 4D2P on the MS surface was well described by the Langmuir adsorption model. The inhibition mechanism was determined by potential of zero charge measurements and some electronic parameters. (C) 2014 Elsevier Ltd. All rights reserved.