A series of compounds derived from 4,5-dihydro-1H-1,2,4-triazol-5-one were synthesized and characterized by spectral data. The 12 new compounds were analyzed for their potential in vitro antioxidant activities by three different methods. Compound 4f showed the best activity for the iron binding. In addition, the compounds 4 were titrated potentiometrically with tetrabutylammonium hydroxide in non-aqueous solvents. The RP-HPLC capacity factors (k) of the series were also determined on a C18 column, with methanol/water as the mobile phase. The correlation between logk with the percentage of methanol in the mobile phase was used for the determination of the logkw values for these compounds. The antimicrobial activities of these compounds were also screened against bacteria and yeast.