A new series of pyrazolyl-imidazolone derivatives 3-6 were synthesized via the reaction of the readily obtainable pyrazolyl-oxazol-5(4H)-one 2 with various aromatic amines namely, 4-aminophenol, ethyl 4-aminobenzoate, 4-aminoacetophenone and 2-aminobenzoic acid in acetic acid including freshly melted sodium acetate. Furthermore, the pyrazolyl-imidazolone 3 on reaction with ethyl 2-chloroacetate, acetic anhydride, benzoyl chloride or benzenesulfonyl chloride afforded the corresponding pyrazolyl-imidazolone derivatives 7-10. The novel compounds were characterized by spectral data and elemental analysis and measured as antioxidant agents using ABTS assay. The candidates showed moderate to good activity compared to ascorbic acid.