A novel and efficient synthesis of substituted 2-(Tetrazolo[1,5-a]quinoxalin-4-yl)-2,3-dihydrophthalazine-1,4- dione has been carried out. The substituted 4-hydrazinyl tetrazolo quinoxalines has been treated with pthalic anhydride. The structures of all the compounds were confirmed by IR, 1H-NMR, elemental analysis and Mass spectroscopy. All the synthesized compounds 5(a-g) were screened for anti-microbial activity. Among all the synthesized compounds 5a, 5c, and 5d and 5e, 5f and 5g showed moderate activity against gram-positive bacterial strains S. aureus and gram-negative bacterial strains E.coli. 5e showed appreciable activity against C. albicans and A. niger organism.