Abstract The successive stabilityconstants of La(III) with somearylhydrazones of benzylacetone (BAAH) and dibenzoylmethane (DBMAH) have been determined potentiometrically following the Bjerrum pH-metric titration. The stabilityconstants of the metal chelates are correlated to the Hammett substituent constant (σ x ) and to the molecular structure. The structures of the complexes have been assigned on