A series of Schiff bases (4a-j) were prepared by reacting 4-amino-5-(1-phenylethyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione and substituted aromatic aldehydes. The chemical structures were confirmed by means of UV, 1H NMR, IR, MS(API-ES) spectral data and elemental analysis. All the synthesized compounds were screened for their antimicrobial activity. Among the tested compounds, Schiff bases with 4-OH and 4-NO2 substituent exhibited remarkable antimicrobial activity against all the tested microorganism.