tThe binding mode and thermodynamic characteristics of the anticancer drug dacarbazine (Dac) withdouble and single stranded DNA were investigated in the absence and presence of Cu(II) using cyclicvoltammetry, square wave voltammetry and fluorescence spectroscopy. The interaction of Dac andDac–Cu(II) complex with dsDNA indicated their intercalation into the base stacking domain of dsDNAdouble helix and the strength of interaction is independent on the ionic strength. The interaction of Dacwith dsDNA in the presence of Cu(II) leads to a much stronger intercalation. The interaction mode ofDac molecules with ssDNA is electrostatic attraction via negative phosphate on the exterior of the ssDNAwith Dac. The binding constants, stoichiometric coefficients and thermodynamic parameters of Dac andDac–Cu(II) complex with dsDNA and ssDNA were evaluated. Comparison of the mode interaction of Dacwith dsDNA and ssDNA was discussed. The decrease of peak current of Dac was proportional to DNAconcentration, which was applied for determination of dsDNA and ssDNA concentration.