A label-free immunosensor based on K3［Fe(CN)6］-chitosan-glutaraldehyde conjugate composite as signal indicator was developed for the easy and sensitive detection of carcinoembryonic antigen(CEA).The signal layer and nafion-modified glass carbon electrode(GCE) was used to wrap CEA antibodies.The morphology and electrochemical behaviors of the modified GCE substrates were characterized by atomic force microscopy(AFM) and cyclic voltammetry(CV),respectively.The result indicated that the response magnitudes of the anodic peak current were directly related to the concentration of CEA.A good linear relationship between decrease of current and logarithm of CEA concentration in the range of 0.005-40.0 ng/mL was obtained,with a detection limit of 1.23 pg/mL.The developed approach showed a high selectivity,and could be applied in the detection of CEA in human serum samples.