Abstract: Objective : To observe the biodistribution of anti-lung cancer monoclonal antibody 1E2 labeled with ¹³¹I in mice bearing Lewis lung cancer and to evaluate the inhibitory effect of this antibody on Lewis lung carcinoma. Methods : The animal model was established by subcutaneous inoculation of Lewis lung cancer cells (1×10⁶)to the right hind legs of C57BL/6 mice. The expression of the 1E2 antigen, also known as carbamoyl phos-phate synthetase 1 (CPS1) on the Lewis lung carcinoma cell membrane, was detected by immunohistochem-istry. The 1E2 monoclonal antibody was radioiodinated with ¹³¹I using the chloramine T method. The labelingratio, radiochemical purity and specific radioactivity of the labeled antibody were detected. After tail intra-venous injection of 18.5 MBq ¹³¹I-1E2, the biodistribution of ¹³¹I-1E2-labeled antibody in mice at different timepoints was observed. After tumor model establishment, all of the mice were randomly divided into 4 groups (n=10). When the tumor reached 0.5-0.7 cm in diameter, intratumoral injection of 0.1ml physiological saline(Blank control), 3μg 1E2 (Positive control), 18.5 MBq ¹³¹I -IgG (Negative control), or 18.5 MBq ¹³¹I-1E2 (Experi-mental group) were administered on day 0, 7 and 14. The tumor size and volume were measured twice aweek before and after treatment. The tumor inhibitory rate was calculated. After 21 days, the mice were sacri-ficed for pathological examination of the tumor. Results : The 1E2 antigen (CPS1) was mostly expressed on tu-mor cell plasmalemma. The labeling ratio of the131 I-1E2 antibody was 67.73%, the radiochemical purity was95.63%, and the radioactivity concentration of131 I-1E2 was mainly distributed to the tumor tissues. The gross umor volume of the experimental group was 0.746±0.153 cm³, the tumor weight was 1.602±0.194 g, and theinhibitory rate was 78.3% at 3 weeks after treatment. A significant difference was found in the gross tumor vol-ume, tumor weight, and inhibitory rate at 3 weeks after treatment between the experimental group and thecontrol groups. Conclusion :¹³¹I-1E2 antibody has the ability to target tumor cells and therefore can effectivelyinhibit tumor growth in vivo.¹³¹I-1E2 possesses potential clinical application value and may become a newdrug for targeted cancer therapy.