Formation constants of the mixed ligand complexes MAL where M=Cu(II), Ni(I1) & Co(I1); A=histidine, 2,2'-bipyridyl or iminodiacetic acid and L = N , 2'-diphenylacetohydroxamic acid and 2,2'-diphenylacetohydroxamic acid have been determined in water-ethanol (50% v/v) medium. Stability constants of ternary chelate were found to be less than the stability constant value of M:L complex. This trend in log K values is explained on the basis of electrostatic repulsion between the primary and secondary ligands. Remarkable stability of ternary chelates (Cu-bip-N,2'-DPAHA) as indicated by the stabilization parameters are explained in terms of electronic effects, geometry of the complex and steric hindrance.