Based on the preparation of an anti-diethylstilbestrol (DES) monoclonal antibody, a simple and convenient indirect competitive enzyme-linked immunosorbent assay (ELISA) method for DES detection has been developed. The monoclonal antibody demonstrated high sensitivity to DES with an IC 50 value of 275 pg mL -1 and detection limit (LOD) of 90 pg mL -1 . The specificity of the assay was studied by measuring cross-reactivity of the antibody with structurally related compounds of ethinyl estradiol (<7%), estrone (<0.1%), estriol (<0.1%), and diethylstilbestrol benzoate (<0.1%). Chicken, fish, shrimp, urine and bile spiked with different concentration of DES were detected by the developed method, and the recovery rates were greater than 79.5%. Intra-and inter-assay variations were about 6%. This method exhibited high stability with a coefficient of variation less than 10% in buffer and in real samples. The LODs in fish/shrimp, liver, feed and urine spiked with DES were 600, 600, 4800 and 600 pg mL -1 , respectively. These results confirmed that the antibody to DES was successfully produced and could be used to establish ELISA methods for DES detection in food producing animals. Diethylstilbestrol (DES; Figure 1) is an orally active synthetic non-steroid estrogen. Since the 1960s, DES has been used as a growth-promoting agent in livestock [1,2]. Later, DES was found to cause cancer and its use was "phased out in the 1970s" by the FAO/WHO. In 1971, DES was reported to be a teratogen when given to pregnant women and has been associated with a rare vaginal cancer in female offspring [3]. On February 5, 1975, the US Food and Drug Administration (FDA) ordered 25 and 100 mg tablets of DES withdrawn; however, it was still illegally used in the livestock industry.*Corresponding authors (email: xirimo2000@yahoo.com; jintliu@sdu.edu.cn)More than 30 years of researches have confirmed that DES is a teratogen, which can cause malformations of an embryo or fetus. Prenatal exposure to DES is associated with an increased incidence of fibroids of adulthood [4,5]. Therefore, the Ministry of Agriculture of the People's Republic of China issued a banned list (Announcement No. 235; http://www. agri.gov.cn/ zcfg/bmgz/ t20060123_540865.htm, accessed on October 24, 2002) of veterinary drugs and announced that the use of DES in food and animal feed was prohibited. The European Union (EU) requires that residual levels of DES in edible animal food should not exceed 2 ng mL -1 [6]. Consequently, a rapid screening method with high sensitivity and