Effective fraction of Cuscuta chinensis were studied using a combination of in vitro and in vivo assays. Estrogen-like activity was determined by uterus growth test in low and high estrogen female model mice. Then MTT assay of the MCF-7 cells was conducted with the medicated serum of the mice. Estrogen-antagonistic effect was also determined by uterus rate of mice. 95%ethanol extracts of Cuscuta chinensis dose of 24 g Â kg- 1 Â d-1 after intragastric administration increased the uterus rate of immature mice; The medicated serum of 24 g Â kg-1 Â d-1 significantly promoted the proliferation of MCF-7 cells. 24 g Â kg-1 Â d-1 95% ethanol extracts + diethylstilbestrol significantly inhibited the growth of the uterus of high estrogen model mice. 95% ethanol extracts were effective fraction of Cuscuta chinensis. The method established is accurate, reliable, which can be used for the further studies on the phytoestrogen material basis of Cuscuta chinensis.