Abstract: Objective: To investigate antipersonnel effectiveness of Hela cell and therapeutic effectiveness of tumor of ¹²⁵I sealed seed source. Method: ¹²⁵I sealed seed source was implanted in tumor of bearingtumor mice, therapeutic effectiveness of tumor and toxicity of blood were observed. Result: ¹²⁵I sealed seed source had antipersonnel effectiveness for Hela cell, and the range of antipersonnel effectiveness was 1.6~2.4mm after 48h irradiation, and controlled patently the growth of tumor, toxicity of blood was not found. Conclusion: ¹²⁵I sealed seed source could control effectively the growth of tumor and obtain therapeutic purpose.