A new series of ten compounds of  1,3,4-oxadiazoles  were  synthesized  by  ring  closure  reactions  of  different acid hydrazides with carbon disulphide and aromatic acids separately. Further, the 2-thio oxadiazoles were treated with aromatic amines to get mannich bases. The structures of the synthesized compounds were consistent with IR, 1H NMR and MASS spectroscopy.  The synthesized compounds were screened by disc diffusion method for their antibacterial and antifungal activity. Among the compounds synthesized 3d, 3e and 5b shown significant antimicrobial activity against both bacterial and fungal strains.