In this work, the corrosion inhibition property of the ethylene glycol methacrylate phosphate (EGMAP) and the polymerized EGMAP also incorporated with sodium montmorillonite (Na+Mt) has been studied. The corrosion inhibition of carbon steel in 1.0 M HCl solution was investigated using electrochemical impedance spectroscopy (EIS) measurements. Data obtained were analyzed to be modeled through appropriate equivalent circuit models. EGMAP is used as the corrosion inhibitor in acidic media, even at very low concentration, the inhibition efficiency increases with concentration and can reach a limiting value (82%) with a concentration of 1.0 × 10−2 mol L−1 of the inhibitor after 48 h of immersion time. The adsorption of EGMAP on the carbon steel surface obeys to the Langmuir's adsorption isotherm. The calculated ΔG°ads value show that the corrosion inhibition of the carbon steel in 1.0 M HCl is mainly controlled by a physisorption process. The polymerization kinetics of EGMAP is favorised under UV-light, by creating highly crosslinked polymerized chains leading to complete conversion degree of the C═C bonds to C─C reached 95% in 45 min. The protective power of this inhibitor also increases in the case of polymerized inhibitor by 80%. The addition of clay in the coating formulation lead to a significant improvement, reaching an inhibitory value of 98%, explained by the adsorption of clay on the surface of the steel. Both formulations present a very advantageous stability of adsorbed layers.