Abstract: Complex of DNA-Fe(Ⅲ) was prepared by mixing 1.00 g·L^-1 DNA solution with 1.00 mmol·L^-1 FeCl₃ solution. A portion (20 μL) of the DNA-Fe(Ⅲ) solution was applied on the surface of the polished GCE, and then 10 μL of 0.50 g·L^-1 CTS solution were dropped onto the GCE to give DNA-Fe/CTS modified GCE electrode after drying at 20℃ for 22 h. Morphology of the modified electrode was characterized by SEM, and its electrochemical behavior and response to H₂O₂ were studied by cyclic voltammetry and the i-t curve. It was found that better electrochemical activity was exhibited by the Fe(Ⅲ) embedded in the DNA/CTS layer and that better electrocatalytic activity for reduction of H₂O₂ at the modified electrode of DNA-Fe/CTS/GCE was observed. Based on these facts, a novel, bio-compatible electrochemical biosensor for H₂O₂ was proposed. Linearity range of this biosensor was found between 0.01 and 2.0 mmol·L^-1 H₂O₂ with value of detection limit (3S/N) of 3 μmol·L^-1.