3-Alkyl(Aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (2) reacted with 3,4-dihydroxybenzaldehyde to afford the corresponding 3-alkyl(aryl)-4-(3,4-dihydroxybenzylidenamino)4,5-dihydro-1H-1,2,4-triazol-5-ones (3). The acetylation and methylation reactions of the latter compounds were investigated, and 4 and 5 type compounds were obtained, respectively. The new compounds were characterized using IR, H-1-NMR, C-13-NMR and UV spectral data. In addition, solutions of the compounds 3a-3e were titrated potentiometrically with tetrabutylammonium hydroxide in three different non-aqueous solvents such as acetonitrile, isopropyl alcohol and N,N-dimethylformamide. The half-neutralization potential values and the corresponding pK(a) values of these compounds were determined in the solvents described above. Thus, the effects of solvents and molecular structure upon acidity were investigated.