A series of 4,5-diaryl-2-[4-(t-amino)-2-butynyl]-2,4-dihydro-3H-1,2,4-triazol-3-ones were synthesized and characterized by infrared spectrum (IR), 1 H-NMR spectra and elemental analyses. Investigation of their antimicrobial activity was performed. Antimicrobial activity profile of the title compounds were evaluated against Gram- positive bacteria, Gram-negative bacteria and fungi. The synthesized compounds displayed different degrees of antimicrobial activities as shown in Table 3. Compound 12 was the most active one. This may be attributed to 4,5-diphenylsubstituent on the triazoline-3 one ring and the nature of the amino groups at terminal acetylenic moiety.