A method is presented for the determination of stability constants of iron(III)-ligand complexes on insoluble polymeric matrices based on a competition chelation reaction for iron(III) of the resin with a soluble chelator. Stability constants (K') were calculated for iron(III)-ligand complexes on DFO-Sepharose gel, HMP-Sepharose gel, AHMP-HEMA resin, and AHMP-DMAA resin. In these resins, desferrioxamine B (DFO, hexadentate ligand) or the 3-hydroxy-2methyl-4(1H)-pyridinone (HMP, bidentate ligand) was bound on insoluble polymeric matrices. The average values (log K') were: 26.6 (DFO-Sepharose); 37.9 (HMP-Sepharose); 27.2 (AHMP-HEMA); and 39.9 (AHMP-DMAA). The stability constants of the insoluble iron(III) complexes on the resins were compared with those of the corresponding soluble iron(III) complexes. The effect of immobilization on the constants was discussed, and it was found that a higher hydrophilicity and stability of a resin resulted in an increase of the stability constant, whereas steric hindrance decreased the stability constant.