Two macrocyclic polyamine ligands and their dinuclear copper(II) (CuII) complexes were synthesized and characterized. In the complexes, two 1,4,7,10-tetraazacyclododecane (cyclen) moieties were bridged by a dipeptide spacer, and CuII as metal ion was coordinated to the ligands to form the novel complexes. These complexes were characterized by UV/VIS, IR, EPR, and ESI-MS analyses. The catalyzed DNA cleavage and DNA binding properties of these complexes were studied under physiological conditions. The effects of complex concentrations, cleavage time, and temperature on the DNA cleavage reactions were systematically investigated. The results strongly suggested that the plasmid DNA (pUC 19) can be cleaved by the dinuclear CuII complexes. At pH 7.0 and 37 degrees, incubating DNA with the complexes for 24 h, all Form I was selectively converted into Form II. At 55 degrees, pH 7.0, the time was shortened to less than 30 min. According to the mechanism experiment, these complexes cleave plasmid pUC19 DNA by oxidative mechanism. The synergistic effect of the CuII ions is important to improve the DNA cleavage.