Abstract: Objective :To study the bilistribution of ¹²⁵I labeled anti-human prostatic specific membrane antigen monoclonal antibody Ed-5 ¹²⁵I-Ed-S) and normal mice IgG in nude mice bearing human prostate cancer, and to explore the feasibility for diagnosis of radioimmunoimaging and clinical use of radiation therapy with ¹²⁵I-Ed-S treat human prostate cancer. Methods :The nude mouse xenografted models with human prostate cancer were established. Anti-human PSMA monoclonal antibody Ed-5 and NMIgG was labeled with I.0.526MBq labeled antibody was injected through tail vein of nude mice xneografted with human prostate cancer. Radioactivity ratio of tumor and nonumor (T/NT), percent injected dosage of every gram tissue (%ID/g) were measured after 24, 48, 72, 120 hours interval of injection, and the biodistribution of labeled antilx>d y were studied. Results :The labelling rate of I-Ed-S was 72.3%, the specific activity of I-Ed-S was 55.2MBq/mg, the radiochemical purity of I-Ed-S was 90.2%, and the inmmunoreactive fraction was 63%. Radioactivity concentration of tumor was found during the 24-120 hours after the I-Ed-S injection. The peak time of I-Ed-S con centration in the xenograft was about 72 hour after injection when the radioactivity ratios between tumor and various tissues were the highest. The highest T/NT radioactivity ratio of tumor/muscle was 6.36. But nonconcentration of I-NMIgG was found, which was distributed evenly in body. Conclusions :The immune activity of the I-Ed-S does not change. The results indicated that I-Ed-S can be located to xenografted human prostate cancer, and it might be used for the imaging and the targeting treatment of prostate cancer.