Oxazolone moiety is the basic core of many synthetic and natural products that have remarkable biological performance. Accordingly, the current book aimed to report efficient and novel routes for the synthesis of a series of compounds containing pyrazolyl-imidazolone ring systems to assess their capacity as antioxidant agents. The book presented the different sections including an introduction to the synthesis, reactions, and biological activity of 2-oxazolin-5-one derivatives, in addition to results, discussion, experimental, and summary sections. Briefly, 1,3-diphenyl-2,3-dihydro-1H-pyrazole-4-carbaldehyde was prepared and used as a reactive precursor for the synthesis of the target compounds. Ammonolysis reactions of the starting compound with aryl- and hetryl amines gave a series of pyrazolyl-imidazolones, in which some of these compounds are reactive in the reactions with chloroacetyl chloride, acetic acid, anhydride, oxazolone. The synthesized compounds revealed remarkable antioxidant potency using ABTS free radical assay depending on the efficiency of the compound to trap the ABTS free radicals.