Abstract: It is difficult to synthesize the complexes of rare earth ions with meso-tetra(4-sulfophenyl)porphyrin(TPPS)in aqueous solution.Eu(Ⅲ)can form complexes with carboxylic acids, such as acetic,tartaric, malonic, gluconic, citric acids and EDTAwith different stability constants,and exhibits irreversible or quasi-reversible redox peaks in cyclic voltammograms.TPPS, which adsorbed on Hg electrode,exerts catalytic effect on the redox behvior of Eu(Ⅲ)-acetic, tartaric, malonic acid complexes by changing the irreversible process to a reversible one, but the Eu(Ⅲ)-TPPScomplex was not formed.The mechanism of such a catalytic effect has been discussed.

Key words: TPPS, Eu(Ⅲ)-carboxylic acid complex, Electro-catalytic effect