The inhibiting properties of 2-Amino-1-(4-aminophenyl)-1H-pyrrolo(2,3-b)quinoxaline-3-carbonitrile (AHPQC) were examined of C38 steel corrosion in molar hydrochloric acid using electrochemical techniques. Impedance data displayed the AHPQC inhibits C38 steel corrosion becoming the adsorbate at metal/electrolyte interfaces. Polarization study indicated that AHPQC is an anodic-cathodic inhibitor. The inhibition efficiencies of AHPQC calculated by both methods reaches 91%. The Langmuir adsorption isotherm was observed for the AHPQC adsorption and its adsorption is realized by physical adsorption; due to the protonated forms of the AHPQC molecule in acid medium. XPS technique was used to discuss the mechanism for the adsorption process of the AHPQC molecule.