[en] An advanced separating technique is being used for radioimmunoassay (RIA). It is simple, rapid and stable. The separating agent is prepared by utilizing polymerization of monomer acrylamide and acrylic acid for producing carrier microparticle with carboxy group. Then using 1-ethyl-3-(3-dimethelaminopropyl) carbodimide as coupling agent, the carboxy group is covalently coupled to the amino-group of antibody to form solid antibody microparticle. The solid antibody microparticles have been prepared for T₃, T₄ and second antibody. The suspensibility and stability towards temperature as well as the tightness of the precipitate in RIA were evaluated, and the nonspecific binding is lower than 2∼3%, the within-assay cv < 5% and between-assay cv < 15%