Abstract: The objective of this study was to evaluate the effects of estradiol valerate(EV)on the estrogen receptor expression and the pathological changes of tissues in uterus, vagina and breast of ovariectomized rats, and investigate the estrogen-like mechanism. HE method was used to determine the tissue pathological changes; the protein expression levels of estrogen receptor alpha(ERα)and estrogen receptor beta(ERβ)in mammary gland, uterus and vagina were detected by immunohistochemistry and Western blot. The results indicated that estradiol valerate could obviously antagonize the atrophy of the target organs in ovariectomized rats, and the up-regulated expression of the estrogen receptors in target organs is the possible mechanism of EV induced estrogenic activity.