A magnetocontrolled immunosensing strategy based on flow-injection electrochemical impedance spectroscopy (EIS) was developed for the determination of carcinoembryonic antigen (CEA) in human serum. The immunosensor was fabricated by immobilizing anti-CEA on epoxysilane-modified core-shell magnetic Fe3O4/SiO2 nanoparticles. The detection principle is based on the difference between the resistances measured before and after the antigen-antibody interaction. The performance of the immunosensor and factors influencing this performance were also proposed. The resistance response depended linearly on the CEA concentration over the range 1.5-60 ng/ml, and the immunosensor gave a detection limit of 0.5 ng/ml (S/N=3). Coefficients of variance (CVs) of <9.8% were obtained for the intra- and interassay precisions. The method was successfully applied to the analysis of CEA in human serum. The recoveries obtained by spiking CEA standards into normal serum were 87-113%. The performance of the immunosensor was compared with a commercially available CEA ELISA. Satisfactory results were obtained according to a paired t-test method (t value<t (critical) at the 95% confidence level). Importantly, the proposed immobilization protocol could be further developed to immobilize other antigens or biocompounds. Figure This study introduced a magnetocontrolled electrochemical immunosensing strategy based on antibody-functionalized magnetic core-shell Fe3O4/SiO2 nanoparticles for the determination of carcinoembryonic antigen in human serum.