The distribution equilibria of six beta-diketones and their iron(III) complexes between Triton X-100 micellar and bulk aqueous phases at 298 K were measured spectrophotometrically. The partition constant of the extractants and the complexes, and the extraction constant of iron(III) in the micellar system were obtained simultaneously by a successive approximation calculation on the basis of a simple two-phase partition model. The values of partition constants for the extractants and for the complexes were compared to those obtained in conventional hexane-water and diethyl ether-water systems. The solute-solvent interaction due to the solvation of the acidic proton with oxygen atoms in the polyoxyethylene moiety was estimated in the experiments for the extractants, The effect of steric hindrance in the polyoxyethylene layer due to the formation of a hydrogen-bonded framework in the region was also observed. Hence, the extractants having phenyl substituent groups were mainly distributed in the nonpolar "core" region of the micelle while those having no bulky group or having a polar group in the substituent would penetrate into the polar "mantle" region. The extractability of the complexes with the extractants having trifluoromethyl groups was lower than that without the substituent group. Water molecules which penetrated into the micelle and formed a hydrogen-bonded framework would disturb the solubilization of the complexes with ligands having trifluoromethyl substituents in the structural region due to the low wettability of the substituent.