In the present study, 3-alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (1a, b, d-g) reacted with 3-phenoxybenzaldehyde to afford 3-alkyl(aryl)-4-(3-phenoxy-benzylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-ones (2a, b, d-g). Then, the acetylation reactions of compounds 2a and 2d-g were investigated. The structures of 11 new compounds were established from the elemental analysis, IR, H-1 NMR, C-13 NMR, MS, and UV spectral data. The synthesized compounds were analyzed for their in vitro potential antioxidant activities in three different methods. Compounds 2f and 3d showed best activity for the iron binding. Moreover, the compounds 2 were titrated potentiometrically with tetrabutylammonium hydroxide in four non-aqueous solvents (isopropyl alcohol, tert-butyl alcohol, acetonitrile, and N,N-dimethyl formamide). Thus, the half-neutralization potential values and the corresponding pK (a) values were determined in all cases. Furthermore, these 11 new compounds and 13 recently reported 3-alkyl(aryl)-4-(2-thienylmethyleneamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (4a-g) and 1-acetyl-3-alkyl(aryl)-4-(2-thienylmethyleneamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (5a, b, d-g) were screened for their antimicrobial activities.