The inhibition effect of 2-mercaptobenzothiazole (MBT) on the corrosion of steel (API SL X52) in 1 M H2SO4 was investigated by electrochemical and theoretical methods. The results of the investigation show that this compound has excellent inhibiting properties for steel corrosion in sulphuric acid and the inhibition efficiency increases with the increase in inhibitor concentration. The adsorption of the inhibitor on the surface of steel was found to obey a Langmuir adsorption isotherm. The effect of temperature on the corrosion behavior of steel without and with the inhibitors was studied, and the activation and thermodynamic parameters were calculated. Ab initio quantum chemical calculations at the density functional theory (DFT) level were performed to correlate electronic structure parameters of MBT and its different tautomers and conformers with its inhibition performance. The quantitative structure activity relationship (QSAR) approach was also used to correlate the quantum chemical parameters with the experimentally determined inhibition efficiencies.