2-(8-hydroxyquinoxalin-5-yl)acetonitrile (QIN3) was tested as corrosion inhibitor for carbon steel in 1.0 M HCl by using polarization and electrochemical impedance spectroscopy (EIS) at 303-333K. The inhibition efficiency was found to increase with increase in QIN3 concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process were calculated and discussed. Potentiodynamic polarization curves indicated that the quinoxaline derivative as mixed-type inhibitor. Impedance measurements showed that the doublelayer capacitance decreased and charge-transfer resistance increased with increase in the inhibitor concentration and hence increasing in inhibition efficiency. The quantum chemical calculations were performed at the density functional theory (DFT) level using B3LYP functional with the 6-31G (d).