Objective To investigate the effects of copulation abstinence on estradiol levels and estrogen receptor-α(ERα) expression in the mammary gland of adult female rats. Methods Twelve 8-week-old female SpragueDawley (SD) rats were randomly divided into two groups: control(copulation) and copulation abstinence. Histological changes of the mammary gland tissue samples was assessed by light and electron microscopic methods and ERα protein was detected by immunohistochemistry and Western blotting analysis. The estradiol levels in serum and mammary gland tissue were measured by radioimmunoassay. Results After a 60-day abstinence period, mammary estradiol levels were reduced (EM>P/EM><0.05). Moreover, ERα protein in the mammary gland tissue was downregulated (EM>P/EM><0.05). No morphological changes was observed in the mammary tissue sections. Conclusion Our results indicate sexual abstinence induced dec