1H-indole-2,3-dione and its derivatives were reacted with 4-amino-N-(5,6- dimethoxypyrimidin-4-yl)benzenesulfonamide to form Schiff’s bases and the Mannich bases of these compounds were synthesized by reacting them with formaldehyde and piperidine. All the compounds were characterized by means of their IR, 1H NMR spectroscopic data and elemental analysis. The antimicrobial activity of these compounds was evaluated by tube dilution method. All compounds showed considerable enhanced antibacterial activity (low MIC) against all bacteria when compared to reference drug sulfadoxine. None of the compounds was active against C. abony. None of the compounds showed antifungal activity.