In the present paper the interaction mechanism and mode of biologically active cysteine dipeptide (Cys-Cys) with DNA was studied by UV-Vis spectrophotometry and fluorescence spectroscopy using ethidium bromide as a fluorescence probe. The results showed that in the buffer solution of Tris-HCl (pH 7.20),at low concentration of Cys-Cys,the ultraviolet spectrum of DNA-Cys-Cys system produced hypochromic effect with increasing the concentration of Cys-Cys. When the concentration of Cys-Cys increased to some high extent,the ultraviolet spectrum of DNA-Cys-Cys system produced hyperchromic effect. Salt-effect experiment showed that the interaction is liable to be affected by the ionic strengths,suggesting the existence of electrostatic binding between Cys-Cys and DNA. The fluorescence of EB-DNA had quenching effect with increasing the concentration of Cys-Cys,and the Stern-Volmer equation indicated that the quenching process was a static one. According to the Lineweaver-Burk equation the binding constant was determined to be 1.640×104 L·mol-1. From the above results it can be concluded that the interaction mode of Cys-Cys with DNA was mainly electrostatic binding. These findings could contribute to further investigation on the mechanism of oligopeptides interaction with DNA.