In the present investigation, a series of ternary copper(II) complexes anchored branched polyethyleneimine (BPEI), [Cu-(phen)(L-AA)]NO 3 -a-BPEI with three different degree of anchoring were synthesized by ligand substitution method and characterized (where, Phen-1,10 Phenanthroline, AA: ala-Alanine (1), gln-Glutamine (2), ile-Isoleucine (3), leu-Leucine (4) and pro-Proline (5). Interactions studies of copper(II) complexes anchored BPEI (1-5) and their precursor analogues with serum albumins have been investigated by different spectroscopy techniques. The calculated binding constant values indicate that the binding affinities among the copper(II) complexes anchored BPEI are in the order of complex 3 > 4 > 5 > 1 > 2. Besides, the binding affinities of copper(II) complexes anchored BPEI increased with the increasing degree of anchoring of copper(II) complex units in the BPEI polymer chain. The thermodynamic studies confirm that the ordinary copper(II) complexes underwent hydrophobic mode of interactions with serum albumins whereas the copper(II) complexes anchored BPEI (1-5) undergo electrostatic interactions predominantly along with some hydrophobic force. Finally, the circular dichroism spectral studies confirmed that the copper(II) complexes anchored BPEI (1-5) can bound with the amino acid residues of the main polypeptide chain of the BSA/HSA and destroyed their hydrogen-bonding networks, resulting in some unfolding of the polypeptides of serum albumins.