A potentiometric immunoelectrode with non-labeled anticancer antigen CA 15-3 antibody used for determinating CA15-3 was reported. firstly, the anti-CA15-3 antibody was immobilized on the surface of polyvinyl chloride-bovine serum albumin membrane, which was activated previously. Secondly, CA15-3 was added on the surface of the antibody membrane to form the antigen-antibody complex. Lastly, the complex membrane was used to assemble an immunoelectrode with an Ag-AgCl inner electrode. The potential of the complex membrane was measured with a pH meter. The response was linear over the range of 15～240　U／mL with a correlation coefficient of 0.9998. Other common antigens in human serum did not interfere with the determination of CA15-3. The mechanism of potential response was explored.