The objective of this work is to synthesize and evaluate the performance of pentaglycidyl ether pentaphenoxyphosphorus (PGEPPP) as a corrosion inhibitor of C38 steel in a 1 M hydrochloric acid solution. In these evaluations, we were using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and we will finish these studies by surface analysis using the scanning electron microscope (SEM) coupled with EDS. The results obtained were in good agreement, showing a significant increase in the inhibition efficiency (IE%) with the increase in the concentration of the inhibitor tested. It reaches a value of 97% for a concentration of 1 mM of PGEEPPP. The potentiodynamic polarization measurement indicates that the PGEPPP acts as a mixed-type inhibitor, thus thermodynamic parameters obtained from electrochemical impedance curves showed that adsorption of PGEPPP epoxy resin to the surface of C38 steel obeyed the Langmuir isothermal model and that the adsorption mechanism is physics. Analysis of the metal surface by SEM/EDS shows the formation of an inhibitor film as a barrier against corrosion of the C38 steel in a solution of 1 M HCl acid. DFT and Monte Carlo simulation studies revealed a good association with the experiment results.