A phytoestrogen composition comprising an extract of Chinese licorice root (Glycyrrhiza uralensis Fisch), liquiritin or isoliquiritin isolated therefrom, which show estrogen activity and inhibitory effect on proliferation of cancer cells, as an effective ingredient. The Chinese licorice root extract, as well as liquiritin or isoliquiritin isolated therefrom, show estrogenicity but not androgenicity, suppress activity of the endocrine disruptor bisphenol-A and inhibit proliferation of cancer cells, e.g., breast cancer cells. The composition is usefully employed as a phytoestrogen for hormone replacement therapy and/or prevention and treatment of breast cancer.