Interaction of ribavirin with CT-DNA was investigated by emission, absorption, circular dichroism, and viscosity studies to determine the binding mode and binding constant of this drug with DNA. The calculated binding constant, Kb
, obtained from UV-vis absorption studies was 4.6×103 M
−1. In fluorimetric studies, the enthalpy (ΔH<0) and entropy (ΔS>0) of the reaction between ribavirin and CT-DNA showed a hydrophobic interaction. In addition, in the circular dichroism spectrum, the drug induces a B→A structural transition of CT-DNA. These results demonstrate that ribavirin interacts with CT-DNA via the groove binding mode. It was observed that the drug has ability to cleave supercoiled plasmid DNA.