4-(Isatin-3-ylideneamino)benzoic acid, was synthesized and converted into 4-(isatin-3-ylideneamino)benzoyl chloride. Hydrazinolysis of the acid chloride afforded4-(isatin-3-ylideneamino)benzohydrazide. The latter compound was used as a key precursor for the synthesis of pyrazole, triazole, phthalazine, thiadiazole, and oxadiazole derivatives via its reaction with different electrophilic reagents. Structures of all synthesized compounds were elucidated from FT-IR, 1H-NMR, mass spectroscopy and elemental analyses. Some of the synthesized heterocycles were screened against selected microbes to test their antimicrobial activity. Keywords: Isatin schiff's bases, benzohydrazide, thiadiazole, pyrazole, antimicrobial activity.