The anti-AFP antibody is immobilized on the surface of PVC-BSA(bovine serumalbumin) membrane, which has been activated by NH2OH·HCl solution. The immunosen-sor consists of such a membrane with added AFP and Ag-AgCl internal electrode. It showedlinear response over concentration range of 10-300μg/L and potential difference(△E) of 15~20 mV for 300μg/L of AFP. Other common antigens in human serum do not interfere withAFP's determination.