Structural modification of the front line antitubercular drug isoniazid provide a lipophilic adaptations of the drug in which hydrazide moiety of isoniazid is replaced by 1,3,4-oxadiazole heterocycles to eliminate in-vivo acetylation by arylamine N-acetyltransferase which results to form inactive acetylated drug. In the present study a series of sixteen oxadiazole derivatives were synthesized and characterized by (IR, 1H NMR, 13C NMR and Mass spectral) studies. All the synthesized compounds were evaluated for their antimicrobial activity by broth dilution method against two Gram positive strains (Bacillus subtilis and Staphylococcus aureus), two Gram negative strains (Pseudomonas aeruginosa and Escherichia coli) and fungal strain (Candida albicans and Aspergillus niger). The minimum inhibitory concentration of the compounds was in the range of 1.56-50 μg ml-1 against bacterial and fungal strain. The results revealed that all synthesized compounds have a significant biological activity against the tested microorganisms. Among the synthesized derivatives 4g, 4h, 4m and 4p were found to be most effective antimicrobial compounds.