The purpose of this study was to develop a novel synthetic stabilizer of enzyme-linked antibody in the enzyme-linked immunosorbent assay (ELISA). The watersoluble amphiphilic phospholipid polymer, poly[2methacryloyloxyethyl phosphorylcholine (MPC)-co-styrene (St)] was synthesized, and its stabilizing functions for the antibody were compared with conventional stabilizers of the antibody conjugated with enzyme (enzyme-antibody conjugate), such as bovine serum albumin (BSA) and casein. In the absence of the stabilizer, the remaining immunologic activity decreased to about 10% of its initial value after 37 days. The same tendency was observed even when the enzymeantibody conjugate in 1.0 wt % BSA solution was used as a stabilizer. In 1.0 wt % casein solution, the immunologic activity decreased to 29% of the initial value after 37 days. On the other hand, in 0.1 wt % and 1.0 wt % poly(MPC-co-St) solution, the activity remained 74% and 92% of the initial value, respectively. The effects of poly(MPC-co-St) on the stabilization of the enzyme-antibody conjugate depended on the concentration of poly(MPC-co-St). During the ELISA procedure, not only did poly(MPC-co-St) have no effect on the reaction between the antigen and the antibody, but it also had no effect on the reaction between the enzyme and the substrate. These results indicate that poly(MPC-co-St) has the ability to suppress the denaturation of protein, enzyme, and antibody. We concluded that water-soluble poly(MPC-co-St) is an effective synthetic stabilizer in the ELISA.