In this study we report on the estrogen activity of silkworm pupa and herb extracts in vitro. The estrogenic activity of these resources was investigated by competition binding assays with estrogen receptor $alpha(ER{alpha});or;ER{eta}$, and viability of MCF-7 cells, a human breast cancer cell line. Saturation ligand-binding analysis of $ER{alpha};and;ER{eta}$ revealed that all plant extracts competed with estrogen ligand for binding to both ER subtypes with a similar preference and degree and competed stronger with ligand for binding to $ER{eta};than;to;ER{alpha}$. The highest $ER{alpha}-binding$ sample was silkworm pupa aqueous extract The highest $ER{eta}-binding$ sample was silkworm pupa oil. These samples were further tested for bioactivity based on their ability to regulate cell growth rate in ER(+) breast cancer cell line, MCF-7 cells. Our studies showed that silkworm pupa, soritae, sesame, yam, pueraria, malt, ginseng, Polygonum multiflorum, and Curcuma longa significantly stimulated the growth of MCF-7 cells (P<0.05). In summary, these results suggested that silkworm pupa and herbs might be useful as potential phytoestrogens.