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Purpose: Immune checkpoint inhibitors (ICIs) targeting tumor-specific PD-1/PD-L1 significantly improve the overall survival rate of patients with advanced cancer by reactivating the immune system to attack cancer cells. To explore their tumor killing effect, we used the radionuclide iodine-131 ( 131 I) to label the anti-PD-L1 antibody Atezolizumab ( 131 I-PD-L1 mAb)., Method: We prepared the radioimmunoassay molecular probe 131 I-PD-L1 mAb by the chloramine-T method and evaluated its affinity using Lewis lung cancer (LLC) cells. The uptake of 131 I-PD-L1 mAb by transplanted tumors was examined through SPECT and its in vivo distribution. We then compared the in vitro and in vivo anti-tumor efficacy of groups treated with control, PD-L1 mAb, 131 I-PD-L1 mAb, and 131 I-PD-L1 mAb + PD-L1 mAb combined treatment. We performed H&E staining to examine the changes in tumor, as well as the damage in major tissues and organs caused by potential side effects. The anti-tumor mechanism of 131 I-PD-L1 mAb was analyzed by Western blot, RT-qPCR and immunohistochemistry (IHC)., Result: 131 I-PD-L1 mAb was highly stable and specific, and easily penetrated into tumor. 131 I-PD-L1 mAb suppressed cancer cell proliferation in vitro, and inhibited tumor growth in vivo by inducing ferroptosis, thus prolonging the survival of experimental animals while demonstrating biological safety., Conclusion: Therefore, our study suggested that 131 I-PD-L1 mAb affected the expression of tumor-related factors through β-rays and thus promoted ferroptosis in tumor. Combined treatment showed better anti-tumor effect compared to single ICI treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)