Abstract: The stabilities of ternary complexes of metal ions (copper, nickel, zinc and cobalt) with beta-hydroxy ketone (BHK) derivatives and benzotriazole (BTAZ) derivatives in 50% water + 50% dioxane medium in 0.1 M KNO3 ionic strength at 25oC using potentiometric pH titrations have been established. The data reveal that the copper forms more stable complexes, which is followed by zinc ion complexes with these ligands. Both nickel and cobalt form complexes with similar stabilities. The stabilities of these complexes are further quantified with Δ log K values, intra-molecular equilibrium constants and percentage of stacking interaction in the ternary systems. The observed positive Δ log K values suggest that the flexible side chain alkyl moiety (butyl group) or aromatic moiety (phenyl group) in BHK ligand overlaps with the fixed aromatic moiety of BTAZ ligand in the ternary complex, which results in the enhanced stabilities for the (BHK-Bu)-Metal(II)-BTAZ and (BHK-Ph)-Metal(II)-BTAZ systems.