Abstract: Interactions between ciprofloxacin (CPFX), Mg²⁺, Mn²⁺ and DNA, and their polarographic and voltammetric behaviour were studied. In 0.1 mol·L^-1 NH₃-NH₄Cl buffer solution (pH 9.2), a new reduction peak was obtained by linear sweep voltammetry with Ep=-1.72 V(vs Ag/AgCl) when adding DNA to CPFX solution, which implies binding of CPFX with DNA. In the presence of Mg²⁺ or Mn²⁺, another new sensitive reduction peak, whose peak potential is more negative (Ep=-1.78 V), was obtained which suggested that Mg²⁺ or Mn²⁺ took part in the interaction between CPFX and DNA resulting in a ternary complex of CPFX Mg DNA. The peak current (ip) is proportional to the concentration of DNA over the range of 1.18×10 ^-4～3. 33×10^-4 mol·L^-1 . In this paper, the properties of the peak current were studied in detail, the result showed that the electrode reaction was irreversible and the ip was influenced by adsorption. The electrode reaction mechanism was also probed into. The CPFX molecule in the complex was reduced on the electrode. Furthermore, CPFX-Mg was shown ot be intercalated between the stacked base pairs of native DNA.