A series of 1,2,4-triazole-based Schiff base heterocyclic compounds (5a-f and 8a-i) and phenethylamines (7a-h) were synthesized and evaluated for antioxidant properties by free-radical scavenging, anti-hemolytic activity, lipid peroxidation, and their protective effects against DNA oxidative damage. Compounds 7c, 7d, 7h, 8b, and 8i showed promising DPPH(•) radical scavenging activity with the level of inhibition between 86.8% and 94%. Compounds 8a, 8b, 8d, 8g, and 8i were effective against the oxidative hemolysis of human erythrocytes and lipid peroxidation, in a dose-dependent manner, with IC50 values in the range of 55.7-80.7 and 53.2-81.2 µg/mL, respectively. Compounds 8a and 8b were effective against oxidative damage on erythrocyte ghost membrane proteins, and 8g and 8i were able to protect against DNA oxidative damage.