Three Pyridazinone derivatives of the type 4,5-dihydropyridazin-3(2H)-ones, N-(4-(6-oxo-5-((5-phenyl-1,3,4-thiadiazol-2-yl)amino)-1,4,5,6-tetrahydropyridazin-3-yl)phenyl) acetamide (4a), 6-(4-Chlorophenyl)-4-((5-phenyl-1,3,4-thiadiazol-2-yl)amino)-4,5-di-hydropyridazin-3(2H)-one (4b) and 6-(4-Bromophenyl)-4-((5-phenyl-1,3,4-thiadiazol-2-yl)amino)-4,5-dihydropyridazin-3(2H)-one (4c) were synthesized. They were characterized by the conventional tools of analysis, Elemental analysis, IR and 1H-NMR spectroscopy. The tools of analysis confirmed the structure of the three prepared compounds. These heterocyclic compounds are chemically stable and possess multi actions for base oil improvement. They are tested as antioxidants for local base oil through the change in total acid number (TAN). They gave good results as antioxidants base oil. Also these three synthesized compounds are tested as corrosion inhibitors for carbon steel in acid medium. The efficiency order for these tested compounds is ranked as follows: 4a > 4b > 4c. Energy of the highest occupied molecular orbital (EHOMO) and lowest unoccupied molecular orbital (ELUMO) for the three prepared compounds were calculated via the Ab initio method. Studying of the quantum chemical calculations of the synthesized compounds showed good matching with the experimental results.