3-alkyl(aryl)-4-[4-(4-methylbenzoxy)benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones (3a, b, d, e, g) reacted with acetic anhydride to afford correspondig 1-acetyl-3-alkyl(aryl)-4-[4-(4-methylbenzoxy)benzylidenamino]-4,5- dihydro-1H-1,2,4-triazol-5-ones (4a, b, d, e, g). The newly synthesized compounds were characterized using by elemental analyses and IR, 1H-NMR, 13C-NMR and UV spectral data. In addition, the synthesized compounds were analyzed for their in vitro potential antioxidant activities in three different methods, including reducing power, free radical scavenging and metal chelating activity. Moreover, antibacterial activity of these five new compounds and eight recently reported 3-alkyl(aryl)-4-[4-(4-methylbenzoxy)benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones (3a–h) were screened agaist seven bacteria such as Bacillus subtilis, Yersinia enterocolitca, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pasterulla multicida and Klebsiella pneumoniae.