Daidzein, an isoflavonoid phytoestrogenic compound found in soybeans, possesses various biological properties. It may induce apoptosis of choriocarcinoma cells in a dose-dependent manner via the mitochondrial apoptotic pathway, in addition, it promotes proliferation and differentiation in osteoblastic OCT1 cells via activation of the BMP-2/Smads pathway. Daidzein exerts neuroprotective effects through the novel extranuclear GPR30 and the classical transcriptionally acting ERβ.