Semen Cuscutae is a kidney-essence invigorating Chinese drug which is widely used in the clinic. In this study, the effects of the flavonoids extracted from Semen Cuscutae (FSC) on the function of the hypothalamus-pituitary-gonads axis in animals was investigated. The results showed that FSC can increase the weight of uterus and promoted the cornification of vaginal epithelial cells in bilateral ovariectomized mice, which suggested that FSC may have estrogen-like activity. In normal female rats, it increased the weight of pituitary, ovary and uterus, but did not increase plasma luteinizing hormone (LH) level. The binding capacity of ovary to 125 I-HCG/LH receptor was significantly elevated the reactivity of luteinizing-releasing hormone (LRH) was increased, and the LRH-induced LH secretion was enhanced in ovariectomized rats. In immature male mice, FSC increased the weight of epididymis and testis, and stimulated HCG-induced secretion of testosterone in short-term cultured rat Leydig cells. It is suggested that FSC can improve the functions of reproductive and endocrine system.