In the present work, we report the one pot synthesis of tetrazole based 3-hydroxy-4H-chromen-4-ones 3(a-g) from 4-(1H-tetrazol-5-yl)benzaldehyde and 2-hydroxy acetophenone using KOH and H2O2 by modified Algar-Flynn-Oyamada reaction under conventional and microwave irradiation conditions. In this technique, flavonols are synthesized without isolating chalcones, in good yields. All the synthesized compounds were characterized by IR, NMR, MS and elemental. All newly synthesized compounds were screened for their in-vitro antimicrobial activity against strains such as Staphylococcus aurous, Bacillus subtilis, Klebsiella pneumonia, Escherichia coli, Aspergillus Niger, Aspergillus flavus, and Fusarium oxysporum. The results of antimicrobial studies revealed that most of the compounds exhibit good activity.