Green method is employed for the synthesis of 5-((1H-benzimidazol-2-ylthio) methyl)-3-(substituted)-1,3,4oxadiazole-2(3H)-thione derivatives by Mannich reaction of 5-((1H-benzimidazol-2-ylthio)methyl)-3-(substituted)-1,3,4-oxadiazole-2(3H)-thione with formaldehyde and different secondary amines . The 1 H NMR, FT-IR and mass spectral studies were carried out to assign the structure of newly synthesized compounds. Amongst all tested new compounds, the antimicrobial assay of piperazinyl substituted oxadiazole derivatives showed good in vitro antibacterial activities.