ABSTRACT The mechanism of the extraction of copper (II), nickel (II), cobalt (II) and thorium (IV) from aqueous buffer media with 4-dinitrobenzoyl1-2, 4-dihydro-5-methyl-2-phenyl-311-pyrazol-3-one (DMPP) in benzene has been investigated. The values of log K*where K*refers to the extraction equilibrium Mn++-nHL ⇌ MDn+ nH+are Cu(II)& lpar; + 0.3), Co(II) (−6.65), Ni(II) (−5.04) and Th(IV) ( + 6.1). Solid complexes synthesized have the composition CuL2· 2H2O, NiL2· 2H2O and ThL4respectively (L = anion of the ligand). DMPP seems to be superior to the corresponding 4-benzoyland 4-nitrobenzoyl derivatives of 2,4-dihydro-5-methyl-2-phenyl1-3 H-pyrazol1-3-one (MPP) and also better than thenoyltrifluoroacetone, the popularly employed fluorinated β-dike tone in the system investigated.