In this report, we present a rapid and highly efficient method for radioactive iodine labeling of trans-cyclooctene group conjugated biomolecules using inverse-electron-demand Diels-Alder reaction. Radioiodination reaction of the tetrazine structure was carried out using the stannylated precursor 2 to give I-labeled product ( I1) with high radiochemical yield (65±8%) and radiochemical purity (>99%). For radiolabeling application of I1, trans-cyclooctene derived cRGD peptide and human serum albumin were prepared. These substrates were reacted with I1 under mild condition to provide the radiolabeled products I6 and I8, respectively, with excellent radiochemical yields. The biodistribution study of I8 in normal ICR mice showed significantly lower thyroid uptake values than that of I-labeled human serum albumin prepared by a traditional radiolabeling method. Therefore I8 will be a useful radiolabeled tracer in various molecular imaging and biological studies. Those results clearly demonstrate that I1 will be used as a valuable prosthetic group for radiolabeling of biomolecules.