New sulfa drugs azo dyes (HL1, HL2, HL3, HL4 and HL5) were prepared by the coupling of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one with the sulfa drugs (sulfadiazine, sulfapyridine, sulfamethoxazole, sulfadimidine, sulfathiazole). The five prepared ligands were characterized by elemental analysis, infrared, mass spectra, and 1H-NMR spectra. The ionization constants of the ligands and stability constants of their Fe (III) complexes were determined potentiometrically in ethanol-water media at 25°C. HL1 ligand has two pKa values while the other ligands (HL2, HL3, HL4 and HL5) have one pKa value. All the ligands form 1:1 metal chelates.