We optimized Origanum majorana (OM) extraction for mild steel corrosion inhibition in neutral 0.5 M chloride medium. The inhibition mechanism evolved in presence of the optimal extract was discussed when calculating the activation energy (Ea), the activation enthalpy (Δ_aH) as well as the activation entropy (Δ_aS). The OM extract molecules were investigated using the density functional theory (DFT) at B3LYP/6-31G(d,p) basis set level. 1-methyl-4-propan-2-ylcyclohexa-1,3-diene alpha-terpinene was predicted exhibiting the most inhibition capabilities.