2-Thiohydantoin (2-THD) was investigated as a corrosion inhibitor of mild steel (MS) in 0.1 M HCl solution using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) measurements. The effects of temperature, hydrogen gas evolution and change of open circuit potential with immersion time were also studied. The MS surfaces with, and without inhibitor has been characterized by SEM. The results showed that 2-THD acts as a mixed type inhibitor in 0.1 M HCl by suppressing simultaneously the cathodic and anodic processes via physical adsorption on the MS surface followed by the Langmuir adsorption isotherm. (C) 2012 Elsevier Ltd. All rights reserved.