Diethylstilbestrol (DES) is a well known, nonsteroidal estrogen with high affinity for the estrogen receptor (ER). Today DES is used to treat breast and prostate cancers. A phosphate derivative of DES [Diethylstilbestrol diphosphate (DES-P)] which is specific to tumor cells consisting alkaline phosphatase enzyme was synthesized and labeled with Tc-99m using tin chloride as reducing agent. In vivo biological activity of Tc-99m labeled diethylstilbestrol phosphate compound (Tc-99m-DES-P) was examined by biodistribution studies on Wistar Albino rats. Statistical evaluation was performed using SPSS 13 program. The percentage (%) radiolabeling yield of Tc-99m-DES-P and quality control studies were done by Thin Layer Radio Chromatography (TLRC). Results showed that, Tc-99m-DES-P may be proposed as an imaging agent for ER enriched tumors such as uterus and prostate and their metastases in bones.