Objective: To assess the effect of short-term gavage of ethanolic extract of Imperata cylindrica L root on the ovarian activity and estrus behavior of female mice. Methods: Eighteen virgin female ddY mice, 8 to 10 weeks of age, weighing 22-25 g with regular estrus cycle, were divided into three groups. Group 1 received 0.5% carboxymethylcellulose, whereas Groups 2 and 3 received the ethanolic extract of Imperata cylindrica L root at 90 and 115 mg/kg body weight (b.w.) per day by gavage for 20 days, respectively. All of the groups were checked before 9 a.m. daily for vaginal cytology to determine the estrus phase. On day 21, the mice were sacrificed to collect serum samples to quantify the concentrations of reproductive hormones using enzyme-linked immunosorbent assay and to determine changes in the reproductive organs based on their reproductive organ weight, histomorphology, and histomorphometry of ovarium and uterus. Results: The reproductive organ weight in the treatment groups was similar compared with that in the control group. The 90 mg/kg b.w. treatment group showed an increase in corpus luteum number when compared with the control group, with few degenerated follicles and diminished oocytes. Moreover, the 115 mg/kg b.w. treatment group showed fewer primordial and primary follicles and an increase in corpus luteum number and a prolonged diestrus phase compared to the control and 90 mg/kg b.w. treatment groups. The histomorphology examination of the uterus showed that the thickness of myometrium and epithelium in the treated animals was similar to the control group. In addition, there was a significant decrease in follicle-stimulating hormone level in the 115 mg/kg b.w. treatment group (P＜0.05). Conclusions: Short-term gavage of ethanolic extract of Imperata cylindrica L root reduces the follicle-stimulating hormone serum level and folliculogenesis.