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The aim of this research is evaluation of the performance of Pistacia khinjukaerial part extract (PKAPE) on the corrosion of carbon steel in 2.0 M hydrochloric acid and 1.0 M sulfuric acid solutions and comparing the differences in the behavior of the extract in these two acidic environments. For this study, the classical method of weight loss and electrochemical methods [open-circuit potential (OCP) time, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS)] were used. Based on weight loss experiments, the maximum inhibition efficiencies of 92.8% and 90.3% were obtained at 2.0 g/L of extract in 2.0 M HCl and 1.0 M H2SO4solutions, respectively. Potentiodynamic polarization results revealed that PKAPE in both examined acidic solutions act as mixed-type inhibitor. Polarization measurements in the temperature range of 25–65 °C were carried out for different concentration to define the effect of temperature on the behavior of the extract. At all investigated temperatures, adsorption of PKAPE on the surface for both acidic media follows the Langmuir adsorption isotherm. Thermodynamic and activation parameters were calculated, and the results inferred that the adsorption of PKAPE on the surface for both acidic solutions is physisorption. Quantum chemical parameters were calculated using the density functional theory (DFT) method for main components of PKAPE to predict their adsorption on the surface.