Due to its electro-donors and electro-attractors sites, the epoxy resin is one of the best corrosion in-hibitors. For these proprieties, this study is for aim to evaluate the performance of pentaglycidyl ether pentaphenoxy of phosphorus (PHQ) resin as corrosion inhibitor. The study performed for the carbon steel in acidic medium (0.5 M H2SO4) at 298 K, by the weight loss and electrochemical methods and the sur-face investigated using SEM/EDS and AFM. The results showed that the corrosion inhibition behavior of inhibitor is excellent in sulfuric acid and the inhibitor efficiency reached a value of 94.23% and 94.96% at 10(-3) M of inhibitor for PDP and PEIS, respectively. The isotherm adsorption shows that our inhibitor obey to Langmuir adsorption and the Delta G(ads)* = -44. 91 kJ/mol means the inhibitor molecules form a chem-ical links with the electrode surface. This type of adsorption called chemisorption. Concerns, the surface analysis indicates that the inhibitor has good protection against the corrosives agents. The experimental result was confirmed by a theoretical study. (C) 2021 Elsevier B.V. All rights reserved.