Abstract: To observe the estrogen-like effects of fulvestrant and its influence on estrogen receptor expression of fulvestrant, this study set control, fulvestrant(500 μg/kg, ip), 17β-estradiol(100 μg/kg, ig)and 17β-estradiol + fulvestrant(100 μg/kg+500 μg/kg)groups. 7 days after dosing, mice were anesthetized; their uterine and vagina were collected. HE method was used to determine morphological changes of the tissues; protein expression levels of estrogen receptor alpha(ERα)and estrogen receptor beta(ERβ)in uterus and vagina were detected by immunohistochemistry and Western blot. The results showed that fulvestrant could obviously influence the growth of the uterus and vagina and expression of estrogen receptor in immature mice. Meanwhile, fulvestrant could significantly inhibit the growth of the uterus and vagina and increase estrogen receptors expression in immature mice. The research showed that fulvestrant has anti-estrogen-like effects, which may be related to the down-regulation of estrogen receptor expression in the target organs.