Abstract: AIM To mimic an important family of selenoenzymes in organism thyroxine (T₄) deiodinases and prepare a selenium-containing abzyme catalyzing deiodination of T₄. METHODS A anti-T₄ monoclonal antibody was generated by hybridoma methodology and converted into a selenium-containing abzyme by the method of chemical modification. The catalytic activity of the enzyme was measured by RIA method. RESULTS The abzyme displayed a marked activity of catalyzing deiodination of T₄ and a higher specificity to the substrate T₄ than that of natural enzyme, and the double reciprocal plots of the initial rates of T₃ formation vs. T₄ concentration yielded a family of parallel lines. The catalytic activity could be sensitively inhibited by 6-propyl-2-thiouracil (PTU), a competitive inhibitor for dithiothreitol (DTT). CONCLUSION An abzyme with the diodination activity was first prepared and the reaction mechanism of the enzyme was bisubstrate ping pong one.