A novel cancerembryo antigen (CEA) electrochemical immunosensor has been constructed using chitosan (CS) as bioactive membranes, gold nanoparticles (AuNPs) and biotinylated horseradish peroxidase (HRP) for signal amplification, and CEA, streptavidin-labeled carcinoembryonic anti-bodies (anti-CEA) immunoreactive complexes as immobilized enzyme-labeled immunoconjugates, accompanied by the optimization of the detection conditions. The effect of different electrochemical responses at different concentrations of CEA can be detected by adopting the competitive enzyme linked immunoabsorbent assay ( ELISA). This novel sensor exhibits such fine properties as with a good linear range (4~16 ng/mL, R2=0.992 7) and a low detection limits of 1 ng/mL.