Amino acids are well known as an effective green corrosion inhibitor. In this study, the authors describe the corrosion inhibition of cysteine (Cys) on the mild steel in sulfuric acid using potentiodynamic polarization, electrochemical impedance spectroscopy. The results suggested that Cys can be used as effective corrosion inhibitors and act as mixed-type inhibitors. The inhibition efficiency reaches 70%. The electronic structure and the inhibition mechanism of Cys was studied using density functional theory (DFT) calculations and Monte Carlo simulation. Molecular adsorption on Fe2O3 surface (110) was investigated using Monte Carlo Simulation. All the steps of quantum calculations and Monte Carlo Simulation were explained in detail and therefore the researchers could follow this study in their future researches.