A new series of [1,2,4]triazolo[3,4-b][1,3,4]thiadiazine derivatives (7) of 4-[(4-amino-5-sulfanyl-4H-1,2,4-triazol- 3-yl)methyl]-2H-1,4-benzothiazin-3(4H)-one (4), were synthesized from (3-oxo-2,3-dihydro-4H-1,4-benzothiazin-4- yl)acetic acid (3). The structures of all newly synthesized compounds were elucidated by elemental analysis, FT-IR, 1H-NMR and mass spectral data. Synthesized compounds were screened for their antioxidant and antibacterial activity and a few of them exhibited significant activity. Among the tested compounds, (3-oxo-2,3-dihydro-4H-1,4- benzothiazin-4-yl)acetic acid (3) posssess antibacterial activity comparable to that of streptomycin. However the activity decreased on derivatization of the acid group.