A novel electrochemical sandwich-type gene sensing system was designed by using a DNA probe (DNA-probe1) immobilized on a gold electrode, the target DNA, and another DNA probe (DNA-probe2) conjugated on a single-walled carbon nanotubes/ferrocene (Fc-SWNT) adduct. In this sandwich-type gene-sensing electrode, the Fc-SWNT adduct could significantly amplify the electrochemical response of the reduction of H2O2. The target DNA could be detected selectively and sensitively based on the much enhanced electrochemical catalytic property of the Fc-SWNT adduct toward H2O2 reduction.