Three novel copper(II), cobalt(II), and nickel(II) complexes of juglone (Jug) containing 1,10-phenanthroline (phen) ligand, [M(Jug) 2 (phen)] (M = Cu(II), 1, Co(II), 2, and Ni(II), 3), have been synthesized and characterized using, elemental analysis and spectroscopic studies. Their interactions with calf thymus DNA were investigated using viscosity measurements, UV–visible and fluorescence spectrophotometric methods. The catalytic activities on DNA cleavage of the complexes 1–3 were studied, which copper complex 1 showed better catalyst activity in the DNA cleavage process than complexes 2 and 3. The in vitro cytotoxic potential of the complexes 1–3 against human cervical carcinoma (HeLa), human liver hepatocellular carcinoma (HepG-2), and human colorectal adenocarcinoma (HT-29)cells indicated their promising antitumor activity with quite low IC 50 values in the range of 0.09 – 1.89 M, which are 75 times lower than those of cisplatin.