© 2020, Springer Nature Switzerland AG.In this investigation, attempts have been made to study the corrosion inhibition properties of three new 2-phenyl-4(3H)-quinazolinone-substituted compounds for mild steel in 1.0 M hydrochloric acid medium. The evaluation was carried out using mass loss, electrochemical impedance spectroscopy, and polarization curves measurement. It is shown that 2-phenyl-4(3H)-quinazolinone-substituted compounds are very good inhibitor’s for mild steel corrosion in 1.0 M hydrochloric acid medium, which acts as mixed-type inhibitors. So, the inhibition efficiency was increased with inhibitor concentration in the order Q-p-Cl > Q-m-Cl > Q-H, which depends on their molecular structures and the chloride para/metapositions. Electrochemical impedance spectroscopy has shown that all compounds act by the formation of a protective film at the metal surface. The correspondence between inhibition property and molecular structure of the 2-phenyl-4(3H)-quinazolinone-substituted compounds is investigated, using density functional theory (DFT). The effect of molecular structure on the inhibition efficiency has been explored by quantum chemical computations and obvious correlations were observed. The binding energies of tested compounds on Fe(110) surfaces were calculated using molecular dynamics simulation. Experimental and DFT study was further supported by molecular dynamic (MD) simulations study.