The objective of this work was to evaluate the efficiency of inhibition the corrosion of two organic molecules derived from benzimidazole, specifically 2-mercaptobenzimidazole (2Mcb) and 2-phenylbenzimidazole (2Fb). The calculations were performed using the Density Functional Theory ( DFT ) at the B3LYP with 6-311+G(d,p) basis set. The quantum parameters correlated with the inhibition efficiency such as the highest occupied molecular orbital energy ( E HOMO ), the lowest unoccupied molecular orbital energy ( E LUMO ) , energy gap ( ΔE ), electronegativity ( χ ), hardness ( η ), the fractions of electrons transferred ( ΔN ), electrophilicity ( ω ) and Fukui indices, were calculated. Calculations were performed in aqueous medium in both protonated and non-protonated forms. Theoretical results were compared with experimental data and a good correlation was found between the chemical quantum parameters and the efficiency of inhibition of the molecules. DOI: http://dx.doi.org/10.30609/JETI.2018-5270