Plants of the genus Taraxacum, commonly known as dandelions, are used to treat breast cancer in traditional folk medicine. However, their use has mainly been based on empirical findings without sufficient scientific evidence. Therefore, we hypothesized that dandelions would behave as a Selective estrogen receptor modulator(SERM) and be effective as hormone replacement therapy(HRT) in the postmenopausal women. In the present study, in vitro assay systems, including cell proliferation assay, reporter gene assay, and RT-PCR to evaluate the m RNA expression of estrogen-related genes(p S2 and progesterone receptor, PR), were performed in human breast cancer cells. Dandelion ethanol extract(DEE) significantly increased cell proliferation and estrogen response element(ERE)-driven luciferase activity. DEE significantly induced the expression of estrogen related genes such as p S2 and PR, which was inhibited by tamoxifen at 1 μmol·L-1. These results indicated that DEE could induce estrogenic activities mediated by a classical estrogen receptor pathway. In addition, immature rat uterotrophic assay was carried out to identify estrogenic activity of DEE in vivo. The lowest concentration of DEE slightly increased the uterine wet weight, but there was no significant effect with the highest concentration of DEE. The results demonstrate the potential estrogenic activities of DEE, providing scientific evidence supporting their use in traditional medicine. Plants, the genus Taraxacum, commonly known as dandelions, are used to treat breast cancer in traditional folk medicine. Therefore, we hypothesized that dandelions would behave as a Selective estrogen receptor modulators (SERM) and be effective as hormone replacement therapy (HRT) in the postmenopausal women. In the present study, in vitro assay systems, including cell proliferation assay, reporter gene assay, and RT-PCR to evaluate the m RNA expression of Estegen-related genes (p S2 and progesterone receptor, PR), were performed in human breast cancer cells. Dandelion ethanol extract (DEE) significantly increased cell proliferation and estrogen response element (ERE) -driven luciferase activity. estrogen related genes such as p S2 and PR, which was inhibited by tamoxifen at 1 μmol·L-1. These results indicated that DEE could induce estrogenic activities mediated by a classical estrogen receptor pathway. In addition, immature rat uterotrophic assay was carried out to identify estrogenic activity of DEE in vivo. The lowest concentration of DEE slightly increased the uterine wet weight, but there was no significant effect with the highest concentration of DEE. The results demonstrate the potential estrogenic activities of DEE, providing scientific evidence supporting their use in traditional medicine.