Abstract: N-succinimidyl 5--(tributylstannyl)-3-pyridinecarboxylate (SPC), a useful linker forlabeling proteins with astatine and iodine radioisotopes, is synthesized in three steps with 5-bromonicotinic acid as a starting material, and is characterized by nuclear magnetic resonance(NMR), mass spectrometer(MS) and high performance liquid chromatography (HPLC). Withthis bi-functional ester, ~(125)I labeled human IgG is performed in labeling yield of approximately30%. Also, the in vitro stability of the prepared ~(125)I-IgG is evaluated.