A novel (N 6O 4) macrocyclic ligand ( L) and its Cu(II) complexes have been prepared and characterized by elemental analysis, spectral, thermal (TG/DTG), magnetic, and conductivity measurements. Quantum chemical calculations have also been carried out at B3LYP/6-31+G(d,p) to study the structure of the ligand and one of its complexes. The results show a novel macrocyclic ligand with potential amide oxygen atom, amide and amine nitrogen atoms available for coordination. Distorted square pyramidal ([Cu(L)Cl]Cl·2.5H 2O ( 1), [Cu(L)NO 3]NO 3 ·3.5H 2O ( 2), and [Cu(L)Br]Br ·3H 2O ( 4) and octahedral ([Cu(L)(OAc) 2] ·5H 2O ( 3)) geometries were proposed. The EPR data of 1, 2, and 4 indicate d 1 x 2 − y 2 ground state of Cu(II) ion with a considerable exchange interaction. The measured cytotoxicity for L and its complexes ( 1, 2) against three tumor cell lines showed that coordination improves the antitumor activity of the ligand; IC 50 for breast cancer cells are ≈8.5, 3, and 4 μg/mL for L and complexes ( 1) and ( 2), respectively.