The inhibition performances of 6-methylquinoxaline-2,3(1H,4H)-dione (MQD) on carbon steel corrosion in hydrochloric acid solution was studied the using electrochemical impedance spectroscopy (EIS) and Tafel polarization techniques. The effects of inhibitor concentration on the inhibition efficiency have been studied. Inhibition efficiency increased with increase in concentration of this compound within the concentration range 10-6- 10-3 M. Changes in impedance parameters (charge transfer resistance, Rct, and double layer capacitance, Cdl) were indicative of adsorption of quinoxaline derivative on the carbon steel surface, leading to the formation of protective films. The adsorption of this inhibitor takes place according to Langmuir`s adsorption isotherm. Potentiodynamic studies revealed that the inhibitor is of cathodic type. The results obtained from the EIS studies showed good agreement with the results from potentiodynamic polarization techniques.