The inhibition performance of 5-tolyl-2-phenylpyrazolo[1,5-c] pyrimidine-7(6H)thione (Tolyl), 5-tolyl-2-pheenylpyrazolo [1,5-c]pyrimidine-7(6H)one (Inon) was investigated as corrosion inhibitors using density functional theory (DFT) at the B3LYP/6-31 + G(d,p) level of theory. The calculated quantum chemical parameters correlated to the inhibition efficiency are: the highest occupied molecular orbital energy(E_HOMO), the lowest unoccupied molecular orbital energy (E_LUMO), the energy gap (ΔE_L-H), dipole moment (μ), ionization energy (Ι), electron affinity (Α), absolute electronegativity (χ), absolute hardness (η), absolute softness (σ), the fraction of electron transferred (ΔN), and the total energy (E_tot) which were calculated. The local reactivity has been analyzed through the Fukui function and local softness indices in order to compare the possible sites for nucleophilic and electrophilic attacks. The success of DFT calculations in predicting the inhibition efficiency was assessed.