Abstract: Provided is a magnetic nanostructure for detecting and isolating cell-free DNA (cfDNA) that including a cationic polymer and a magnetic-nanoparticle-containing conductive polymer. The magnetic nanostructure for detecting and isolating cfDNA according to the subject matter can significantly improve detection and extraction efficiencies of DNA present in a urine, CSF, blood plasma, or blood sample, and exhibits an enhanced sensitivity. Therefore, it is expected that the magnetic nanostructure for detecting and isolating cfDNA according to the subject matter will be used for extracting DNA for use in a genetic mutation diagnosis service as well as for an early cancer diagnosis and cancer treatment.