Abstract: Multi-walled carbon nanotubes (MWCNTs) were dispersed in chitosan (CTS) and dropped on the surface of glassy carbon electrode (GCE), after drying solutions of hemoglobin (Hb), DNA and CTS were successively dropped on the above electrode, to form the composite film modified GCE or named abbreviately as CTS/DNA/Hb/ MWCNTs/GCE. The electrochemical property of the modified electrode was studied by square wave voltammetry and cyclic voltammetry. It was found that DNA in film showed an obvious oxidative peak at the potential of 0.46 V (vs.SCE) in phosphate buffer solution of pH 5.8. Linear relationship between values of oxidative peak current and mass of DNA in the composite film was obtained in the range of 1.0-5.0 μg. Value of detection limit (3S/N) was found 0.5 μg.