A new corrosion inhibitors namely 3,7-dimethylquinoxalin-2(1H)-one (CH3-Q=O) and 3,7- dimethylquinoxaline- 2(1H)-thione (CH3-Q=S) were undertaken and their inhibitive performance towards mild steel corrosion of in 0.5 M sulphuric acid at 20°C has been investigated. The study of corrosion inhibition was conducted by weight loss, polarization curves and electrochemical impedance spectroscopy (EIS) measurements. These studies have shown that CH3-Q=O and CH3-Q=S were with distinguishable inhibition efficiencies in sulphuric acid. Polarization measurements reveal that the CH3-Q=O was cathodic type inhibitor whereas CH3-Q=S was a mixed-type inhibitor. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. Comparable results were obtained by the different chemical and electrochemical methods used. Activation energies of the corrosion process in absence and presence of inhibitors were obtained by measuring the temperature dependence of the corrosion current density. The adsorption of inhibitors on metallic surface in corrosive medium was found to obey Langmuir's adsorption isotherm.