Abstract: Development of ¹¹⁷Sn^m radiopharmaceuticals with radiosensitization ability to the treatment of tumors is valuable since such agents may increase therapeutic effects. In this paper, ¹¹⁷Sn^m(¹¹³Sn) was prepared by irradiation of spectrally pure natural metallic tin grain with reactor thermal neutrons (neutron fluence rate 4×10¹³cm^-2·s^-1) for a period up to 90h, yielding ¹¹⁷Sn^m and ¹¹³Sn with specific activity of 0.13GBq/g and 6.16MBq/g respectively, and meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS₄) was labeled with ¹¹⁷Sn^m (¹¹³Sn) in aqueous solution. The optimized preparation conditions are as follows:pH=2-4, reaction temperature about 100℃, reaction time 30min. Under the recommended experimental conditions, the yield of ¹¹⁷Sn^m-TPPS₄ is higher than 95%. No significant decomposition of the ¹¹⁷Sn^m-TPPS₄ complex solution is observed either during the standing period of 48h after its preparation, or after the dilution of it with physiological saline to 5-15 times at room temperature. A 1∶1 stoichiometry of the ¹¹⁷Sn^m-TPPS₄ complex is obtained by the job’s method.