A copper(II) complex (CuL, 1) with aminothioether ligand and its new inclusion complex with β-cyclodextrin (CuL/β-CD, 2) have been prepared successfully. The binding modes of both complexes with calf thymus DNA were investigated by UV-visible and circular dichroism spectroscopies. Results show that both complexes mainly adopt electrostatic attraction binding mode with DNA and binding constants are (2.02 ± 0.02) × 103 and (1.79 ± 0.05) × 103 M-1, respectively. Both complexes are able to cleave pBR322 plasmid DNA efficiently in the presence...