Objective To explore the biodistribution of 131I-BDI-1 in nude mice model bearing human bladder cancer, and to evaluate the medical internal radiation dose (MIRD) in major tissues and organs of human body. Methods Antihuman bladder carcinoma monoclonal antibodies BDI-1 was labeled with 131I directly by chloramine-T method to prepare 131I-BDI-1. Nude mice bearing human bladder cancer were injected 222 kBq of 131I-BDI-1 via tail vein. Then the mice were sacrificed at different time. Organs and tissues of interest were taken, weighed and radioactive counts were measured. Standard uptake value and ratio of target to non target tissues of 131I-BDI-1 in nude mice bearing tumor were calculated. Standard uptake value by the MIRD of 131I-BDI-1 in human body was calculated by software to estimate the effective dose of 131I-BDI-1 in standard human model. Results The biodistribution data showed that the blood clearance of 131I-BDI-1 was slow, and tumor radioactivity retention was long. The uptake ratio of target to non target tissues was high except tumor to blood. The effective dose of 131I-BDI-1 in standard human model was 1.46×10−2mGy/MBq. Conclusion 131I-BDI-1, can target human bladder cancer EJ and remains in the tumor for long time. The MIRD is reasonable .The result suggests radioiodine labeled BDI-1 may be a suitable agent for bladder tumor imaging and therapy.