Barbituric Acid (BA), Ethyl Barbituric Acid (EBA) and 2-Thiobarbituric Acid (2-TBA) were studied as inhibitors for mild steel (MS) corrosion in 0.5 M HCl solution. Electrochemical studies were performed by means of electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. Inhibition efficiency of these compounds is dependent upon structure and inhibitor concentration. 2-TBA is a better inhibitor than the others. The inhibition efficiency of 2-TBA increases with increase of inhibitor concentration and reached 97.7% at 168 hours. 2-TBA adsorbs on MS surface according to the Langmiur adsorption isotherm. The values of adsorption equilibrium constant (K-ads) and standard free energy of adsorption (Delta G degrees(ads)) were calculated and discussed. To evaluate adsorption mechanism of inhibitor on the steel surface, the potential of zero charge (pzc) of MS was also determined by EIS method.