Five 4-acyl-3-phenyl-5-isoxazolones (AcyPI or HL) including three new compounds, 4-(4-toluoyl)-, 4-(4-fuluorobenzoyl)- and 4-(4-nitrobertzoyl(-3-phenyl-5-isoxazolones (TPI, FBPI and NBPI, respectively), were synthesized. The extraction of aluminium(III), gallium(IH) and indium (III) into benzene with the synthesized AcyPI has been investigated. The acid dissociation constants, Ka, and the partition coefficients, Kν, of AcyPI and the extraction constants, Kax, of their metal complexes were determined. The introduction of an electron-withdrawing fluoro or nitro group to the 4-position of the benzene ring in the acyl moiety of AcyPI was very effective for increasing the Kν. value of AcyPI, but scarcely affects the Kν value. The extracted species were ML3in all the extraction systems, where M denotes the metal ion.