The corrosion inhibition efficiency of 3,7-dimethyl-1-(prop-2-yn-1-yl)quinoxalin-2(1H)-one (DPQO) on carbon steel in 1.0 M HCl solution has been investigated using, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss, and scanning electron microscopy (SEM) methods. The results showed that the inhibition efficiency of DPQO increased with the inhibitor concentration but decreased with temperature. Polarization studies revealed that DPQO acts as a mixed-type inhibitor at 308 K. The inhibitor adsorption on the steel surface obeyed the Langmiur isotherm and the thermodynamic parameters (K_ads, ΔG_ads^ο) were calculated and discussed. The corrosion process in 1.0 M HCl in the absence and presence of DPQO followed first-order kinetics. Activation parameters of the corrosion process (E_a, ΔH_a and ΔS_a) were also calculated from the corrosion rates. SEM results supported the adsorption conclusions. Quantum chemical calculations have been performed using DFT and several quantum chemical indices of DPQO were calculated and correlated with its inhibitive effect.