This study is to explore the effects of quercetin (QUE) on the 3 week-old mice ovarian development and relative hormone levels.  The 3 week-old mice were exposed to QUE (45, 25, and 5 mg·kg⁻¹·d⁻¹) by gavage for 50 days.  The estrous cycle during 50 days and the changes of hormone level such as FSH, LH, etc were monitored.  Moreover, the ovaries were removed after sacrifice.  The organ index was measured, and the ratios of different stages of follicles were analyzed by HE staining.  Furthermore, the proportion of PCNA positive cells during all stages was detected by immunohistochemistry.  The results showed that QUE could increase body weight of mice and reduce the anogenital distance (AGD) to some extent, and was able to disrupt mice’s estrous cycle, but it could not extend or reduce the cycle regularity.  It increased ovarian organ index with a dose-dependent manner.  The proportion of the primordial follicle and secondary follicles rose obviously, and that of mature follicles’, atretic follicles’ and corpus luteums’ reduced, while primordial follicle had no change.  Immunohistochemistry analysis showed that QUE could effectively increase the percentage of proliferating cells in all kinds of follicles.  Serum hormone assay showed that there were significant changes of FSH and LH levels.  In summary, QUE showed an estrogen-like effect on mice’s ovarian development.  The weight of ovary, the proportion of all kinds of follicles, the development of ovarian cells and the level of plasma hormone in mice were altered obviously by oral administration of QUE.