Abstract <p>Compounds with five-membered heterocyclic rings, especially triazole, oxadiazole, and thiadiazole derivatives, attract attention in pharmaceutical chemistry owing to their broad spectrum of biological effects. However, the use of triazole derivatives is limited because of reasons like the risk of toxicity, increased drug resistance, undesirable side effects, and pharmacokinetic deficiencies. In this study, seven new Mannich base 1-(morpholin-4-yl-methyl)-3-substituted-4-(3-hydroxy-4-methoxybenzylideneamino)-4,5-dihydro-1<i>H</i>-1,2,4-triazol-5-one derivatives containing a triazole ring were synthesized by the reaction of 3-substituted-4-(3-hydroxy-4-methoxybenzylideneamino)-4,5-dihydro-1<i>H</i>-1,2,4-triazol-5-one compound with morpholine and formaldehyde. The structures of the obtained compounds were elucidated by FT-IR, ¹H and ¹³C NMR spectroscopic methods. The antioxidant activities of the compounds were evaluated in vitro by three different methods, namely free radical scavenging, reducing power, and metal chelating capacity, and compared with standard antioxidants like α-tocopherol, BHT, EDTA, and BHA. In addition, the antimicrobial activities of the synthesized compounds against six different microorganisms, namely <i>Bacillus cereus</i>, <i>Bacillus subtilis</i>, <i>Pseudomonas aeruginosa</i>, <i>Escherichia coli</i>, <i>Staphylococcus aureus,</i> and <i>Klebsiella pneumoniae</i>, were determined by the agar well diffusion method. The outcomes revealed that the antimicrobial activities of the compounds varied depending on the substituents in their structures.</p>