Objective：To label the fulvestrant （an endocrine therapy drug for breast cancer） with the radioiodine. Methods：The fulves－trant was radioiodine labeled by improved chloramine T method. The paper chromatography was used to detect the labeling rate and the stability of the labeled compound. The column chromatography was used to detect the separation and purification of labeled com－pound. The changes in physicochemical property of the 131I-fulvestrant was detected by mass-spectrography；the combining ability and inhibiting ability of labeled compound to human breast cancer cells MCF-7（ER+） was detected by cell binding assay and MTT assay. Results：When the reaction lasted for 5 min at room temperature at the pH value of 7.5，the radiochemical yield of the radioio－dine labeling to fulvestrant was （62.34±1.80）%，radiochemical purity was （98.6±3.4）%，the half maximal inhibitory concentration（IC50） of 48 h was 35 μCi. The labeled compound was stable and its combining ability to human breast cancer cells MCF-7（ER+） was also retained. Conclusion：The radioiodine labeling to the fulvestrant is successful，and it may be used to develop a new drug for breast cancer.