The extraction of Eu(III) with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the lumines- cence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltrifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β, of the first complexes between tris(β-diketonato)Eu(III) and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu(III) luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu(III), while that in Eu(pta)3PhPO was stronger than EuA3; however, in Eu(tta)3PhPO, it was weaker than Eu(tta)3. The POPO functions as a sensi- tizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu(III) luminescence in the complexes as well as the observation of the extractability of Eu(III) with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu(III) was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence en- hancement. This phenomenon may be due the formation of a strong bond between the Eu(III) and the strong Lewis base leading to more hy- drophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu(III). It was not significant whether the donor atoms were N or O. The extraction of Eu (III) with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the lumines- cence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltrifluoroacetone, Htta, were Used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extracted data, the stability constants, log β, of the first complexes (t-β-diketonato) Eu (III) and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu (III) luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu (III), while that in Eu (pta) 3PhPO was stronger than EuA3; however, in Eu (tta) 3PhPO, it was weaker than Eu (tta) 3. The POPO functions as a sensi- tizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu (III) luminescence in the complexes as well as the observation of the extractability of Eu (III) with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu (III) was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence en- hancement. This it may be due to the formation of a strong bond between the Eu (III) and the strong Lewis base leading to more hy- drophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu (III). It was not significant whether the donor atoms were N or O.