The study aimed to investigate the bio-distribution and radio-immuno-imaging features of [I-131]-herceptin in nude mice with BT-474 breast carcinoma. [I-131]-Herceptin was administrated by tail intravenous injection to the nude mice with BT-474 breast carcinoma. Radiocounting was performed at 4, 12, 24, 48, and 96 h after administration. The activity ratio in the tumor tissue and non-tumor tissue (T/NT) and the radiocounting percentage per gram tissue to the injected dose (%ID/g) were calculated. The nude mice with BT-474 breast carcinoma were also visualized continuously by single photon emission computed tomography at 2, 4, 8, 12, 24, 48, and 96 h after the injection of [I-131]-herceptin. Nude mice with MDA-MB-231 used as the control group were subjected to the same analyses. Clear tumor images were obtained after the injection of [I-131]-herceptin in nude mice with BT-474 breast carcinoma. The images were the clearest at 24 h after the injection and remained clear even at 96 h. The T/NT ratio and %ID/g in the tumor tissues of nude mice with BT-474 were both significantly higher than those of the control group (P < 0.01). [I-131]-Herceptin displays tumors clearly in the nude mice with BT-474 and accumulates well in the tumor tissues.