Abstract: Objective: To study the biodistribution of 99Tcm-luteinzing hormone-releasing hormone (99 Tcm-LHrH) in nude mice bearing human breast cancer, and to evaluate the effect of cancer diagnosis and targeted radiotherapy with 99Tcm-LHrH in nude mice bearing human breast cancer. Methods: LHrH was directly radio labeled with 99Tcm . Twenty-five nude mice were randomly divided into five groups, five in each. Nude mice bearing SK-br3 breast cancer cells were injected with 99Tcm-LHrH by vein caudalis，and sacrificed. Detect the biodistribution of 99Tcm-LHrH and calculated per gram Organization percentage injected dose rate. results: The result showed that radiochemical purity of 99Tcm-LHrH was more than 95%. The ratios of tumor to blood and tumor to muscle were 12. 89 1. 67, and 36. 81 5. 64, respectively. The biodistribution experiment showed that 99Tcm-LHrH uptake by liver，blood, tumor site was higher than by muscle and brain. Conclusions: 99Tcm-LHrH has good specificity to human breast cancer cell. It may be used in the targeted diagnosis and therapy of breast cancer.