A series of novel 3-methyl-7-substituted-4H-1,4-benzothiazine-2-carbohydrazide (3a-e) and corresponding thiosemicarbazides (4a-q); 2-[3-methyl-7-substituted-4H-1,4-benzothiazine-2-yl]-N-(aryl)hydrazine carbothiamide have been synthesized. By the intramolecular cyclization of thiosemicarbazide compounds 4a–q in concentrated H2SO4, thiadiazoles were obtained in high yields and the compounds were tested for antibacterial and antifungal activities against different microorganisms.