Three piperidine derivatives of 2,9-dimethyl-4,7-diazadecane-2,9-dithiol (DDD), NEPDDD, NEMPDDD, and NEMMPDDD, were synthesized and used as catalysts in DNA cleavage. Under physiological conditions, a series of experiments have been done. The effects of DNA cleavage with three ligands were studied under different concentrations, cleavage time, and pH values. The results strongly suggested that the plasmid DNA (pUC 19) can be cleaved efficiently by these ligands. For the cleavage reaction catalyzed by NEMPDDD, Form I DNA could convert to Form II completely, and the DNA-cleavage mechanism involved an oxidative pathway.