A new series of schiff base and aminothiadiazole derivatives of N- substituted phthalimide (I-VI) were synthesized. In this work, the intermediate 4-(1,3-dioxoisoindolin-2-yl)benzaldehyde compound (I), was formed by reaction of 4-amino benzaldehyde with phthalic anhydride in glacial acetic acid(GAA). A series of Schiff bases (IV-VI) was prepared by the reaction of benzidine with compound (I) in ethanol and presence of GAA as a catalyst to form compound (IV) which react with compound (I) and p-nitro benzyldehyde to give compound (V) and (VI) respectively. A new phthalimide thiosemi-carbazone derivative (ll) was prepared by reaction of compound (l) with thiosemi-carbazide HCl in the presence of equimolar amount of sodium acetate. Finally, a new phthalimide containing (1,3,4- thiadiazole ring) compound (III) was formed by bromine mediated “oxidative intramolecular cyclization” of compound (I) in the presence of sodium acetate. All of the final target compounds' structures were successfully synthesized and confirmed using analytical and spectroscopic data. These compounds were identified and confirmed by melting points, TLC, FT IR, and 1H NMR. While the antimicrobial effect of the new derivatives has been assessed in vitro against G-positive, G-negative bacteria and fungi activity. All screened compounds exhibited no activity against G-positive bacteria (Staph. Aureus, and Bacillus subtilis). Many of synthesized compounds displayed moderate effect against “G-negative bacteria Escherichia coli, and Klebsiella pneumonia and against Candida tropicalis”. While the best antifungal activity was obtained from compound I which has high activity against Candida tropicalis.