The protonation constant values of different twelve 3-alkyl(aryl)-4-(p-t-butyl(benzyl/ benzyliden)amino)-4,5-dihydro-1H-1,2,4-triazole-5-one derivatives have been determined in ethanol %50 – water %50 mixtures by spectrophotometric methods. The electronic absorption spectra of different twelve triazole derivatives at various pH values at 190-400 nm intervals were recorded. The calibration of the electrode system was done potentiometrically by Gran’s method. Data were calculated using the linearization method with Henderson-Hasselbach equation. The obtained results are in good accordance with potentiometric values