4,5-Diphenyl-1H-Imidazole-2-Thiol (DIT) as C38 steel corrosion inhibitor in 1 M HCl soluti on was studied by using potentiodynamic polarization and electrochem ical impedance spectroscopy (EIS). Polarization cur ves indicate that inhibition efficiencies of DIT increase with increasing inhibitors concentration. Inhibition efficiency of DIT reached 92.74% at 10 -2 M. The adsorption of DIT on C38 steel surface obeys the Langmuir isotherm. The negative values of ∆ G° ads indicate the spontaneous adsorption of the inhibit or on steel surface.