Corrosion processes are responsible for numerous losses mainly in the industrial scope and the best way to resist the corrosion is a protection. The corrosion inhibitor among the various methods used to avoid or prevent destruction and degradation of metal surface; it is one of the best methods used in the industry. These methods were followed due to their low cost and practice method. The theoretical and experimental experiences have been conducted to calculate the properties of inhibitory substance. Inhibitors showed good aceptance in the industries due to their excellent anti-corrosive proprieties. Nevertheless, many showed a secondary effect on environment. Therefore, the researcher started preparing friendly environmentally inhibitors, such as the organic inhibitors.<br />Mild steel is an alloy form of iron which can undergo corrosion easily in acidic medium. Several methods used in combating corrosion problems, the chemical inhibitors remain the most cost-effective and practical method. Development of corrosion inhibitors based on organic compounds containing nitrogen, sulphur and oxygen atoms are interesting in the field of corrosion and industrial chemistry.<br />Organic compounds are the most efficient inhibitors due to containing electronegative functional groups and π-electrons in triple or conjugated double bonds. The dsorption on the metal surface depends mainly on the physicochemical properties of the inhibitor, such as the functional group, molecular electronic structure, electron density at the donor atom, p orbital character and the molecular size. Organic compounds donate electrons to unoccupied d orbital of metal surface to form coordinate covalent bonds and can also accept free electrons from the metal surface by their antibonding orbital to form feedback bonds, which is considered excellent corrosion inhibitors. However, barbituric acid is considered the main substance that enters the formation of inhibitory substance so the barbituric acid is a strong acid in aqueous medium with an active methylene group and can be involved in Knoevenagel type condensation reaction. Barbituric acid is a cyclic amide upppsed as the parent compound to produce barbiturates that act as central nervous system depressants.<br />Molecules that are planar tendency to adsorb at the metal surface than molecule that has less planar geometry. Quantum chemical calculations have been widely used to study reactive mechanism and were also an effective tool in the analysis and elucidation of many experimental observations. So, they have proved to be apowerful tool for studying corrosion inhibition mechanism.<br />In recent decades, quantum chemistry calculations have been used for various chemical fields such as reaction pathway analysis and spectroscopic assignments due to the theoretical developments, especially accuracy improvement of functionals in density functional theory (DFT), and high-speed parallel computers. However, the functionals in DFT should be appropriately employed for a target system or phenomenon because its reproducibility depends on the functionals used. Therefore comparison among obtained results with available experimental data or high-level computations is necessary to avoid misleading. <br /><br /> <br />