Polystyrene-based chelate resin, functionalized by tridentate iminodiacetic acid moieties, has the special ability to increase the specific surface area by complexing with multivalent cations and drying after being washed with the organic solvent miscible with water. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the structure of the chelate resin-Fe(II) and -Fe(III) complexes. The EXAFS data for the chelate resin-Fe(III) complex, which has the largest surface area among the various chelate resin-metal complexes investigated, indicate that the Fe(III) ion has the coordination number of 6 with one iminodiacetic acid moiety and three water molecules, which are retained in a dry state. The surplus positive charge, due to the 1:1 complexation of Fe(III) ion with IDA moiety (-2), repulses other surplus positive charges or Fe(III) ions, resulting in preventing the pores from shrinking and in making the surface area quite large. In contrast, in the case of the chelate resin-Fe(II) complex, the coordination number of the Fe(II) ion is 4, suggesting the coordination of Fe(II) to four or five oxygen and/or nitrogen atoms including one or two iminodiacetic acid moieties and one water molecule which cannot be removed by drying after being washed with the solvent. It has also been confirmed that the chelate resin-Fe(II) complex can adsorb an NO gas by coordination of NO to the vacant orbital of Fe(II) ions, resulting in the 5-coordinate structure.