To synthesise and investigate the antimicrobial activity of 4-prop-2-ynyl-3-butyl-benzo- [e][1,2,4]-thiadiazine-1, 1- dioxide. The reported antibacterial activity of 3- butyl-4Hbenzothiadiazine dioxide encouraged the investigation of the possible interaction of propynyl bromide and the corresponding antibacterial activity. The alkylation of 3-butyl- 1, 2, 4-benzothiadiazine 1, 1-dioxide 5, with propynyl bromide was accomplished using anhydrous K2CO3 in DMF. The synthesized 4-prop-2-ynyl-3-butyl-benzo- [e][1,2,4]- thiadiazine-1, 1-dioxide was tested for antibacterial activity using clinical isolate of Staphylococcus aureus, Bacillus subtilis, Streptococcus pneumonia, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumonia. The spectroscopic data unequivocally characterized 4-prop-2-ynylbutyl- 4H-1,2,4-benzothiadiazine-1,1-dioxide and it possesses no antibacterial activity against all the clinical isolates compared to the commercial antibiotics used in this study. The compound showed no activity against all the tested strains of organisms.