The electrochemical behavior of complex of Cu (II) with 3- hydroxy-3-m-tolyl-1-p-sulphonato (sodium salt) phenyltriazene (HTST) was studied . It was observed that HTST forms 1:3 complex with Cu(II) in between pH 6.5 to 7.1 . It was found that the reduction process of Cu(II)- HTST complex is two electron reversible reduction process.The logarithm value of stability constant of 1:3 Cu(II)-3-hydroxy-3-m-tolyl-1-p-sulphonato(sodium salt) phenyltriazene complex is 13.02. The present paper also reports antifungal activity of hydroxy-3-m-tolyl-1-p-sulphonato(sodium salt) phenyltriazene, and its Cu (II) complex against Rhizoctonia solani, the fungi causing disease in fennel. The result has been expressed as percentage inhibition (PI) of mycelial growth as well as sclerotium formation at 500 ppm for both ligand as well as complex. The result shows that PI value in complex is 88.03 whereas for ligand 78.63. Thus it is clear that complex is better in activity against the fungi compared to its respective ligand. The result has been interpreted in terms of theory of drug action proposed by Paton.