The inhibition performance of quercetin for C38 steel in1.0MHCl was evaluated by electrochemical measurements: impedance spectroscopy and polarization curves tests. Results obtained reveal that the quercetin acts excellently as a corrosion inhibitor for C38 steel in 1.0 M HCl. The inhibition efficiency increases with the concentration of the inhibitor to reach 98.2 % at 2.10-6M of the quercetin. Polarization curves showed that the quercetin behaves as a mixed-type inhibitor. The adsorption of the inhibitor on the carbon steel surface obeyed the Langmuir adsorption isotherm. The effect of temperature on the corrosion behavior of carbon steel in 1M HCl was also studied. EIS spectra exhibit one capacitive loop and confirm the inhibitive ability. Data obtained from EIS technique, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit model; a constant phase element (CPE) has been used. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated and discussed. Quantum chemical parameters were calculated using ab initio and DFT methods to find a good correlation with the inhibition efficiency. A good agreement was found between the theoretical calculations and experimental observations.