Objective : The aim of this study is to determine the pharmacological effects and the estrogenic properties of Amaranthus viridis leaves on the reproductive function of animal model (female rat). Methods : Vaginal smears performed 9 days before treatment allowed to select female rats having alternated on two cycles a regularity. Thereafter, the selected rats were administered by gavage daily for 28 days taking care of smear every morning at 7am from the first day of treatment follow the evolution of the cycle. For this study 20 nulliparous rats, 2 months old, weighing between 120-150 g. The first group (control) was administered with olive oil and the other three batches received respectively the doses 200, 400 and 600 mg/kg of the methanolic extract of Amaranthus viridis. At the end of the 28-day treatment, ovary and uterine horn were removed, histological and hormonal parameters were studied for determine pharmacological effects of methanolic extract of Amaranthus viridis. Results : The extract caused a disturbances of the cycle according to the doses administered. Disturbances at doses 200 and 400 mg/kg PC are significant. The calculation of the total duration of the different phases of the cycle revealed very significant increases in the estrous phase (P<0.01) by 22.79 % and 17.13 % at the respective doses of 200 and 400 mg/kg b.w compared to control. Non-significant difference was recorded on FSH, LH and estradiol level. On progesterone level, administration of the methanolic extract showed a significant difference at dose of 600 mg/kg b.w compared to control. On histological structure of the ovary, the presence of active and degenerate corpus luteum, secondary follicles depending on the dose administered were recored. Conclusion : The results showed that the methanolic extract of Amaranthus viridis contain estrogenic substances or estrogen-like substances according to a dose-dependent mechanism, with high estrogenic potential at doses of 200 and 400 mg/kg b.w . Keywords: vaginal smears, Amaranthus viridis, methanolic extract, histology