Background: Phytoestrogens in edible plants, including soybean isoflavones and pomegranates, have been used for alleviation of premenopausal/postmenopausal syndromes and osteoporosis. Mauritia flexuosa (moriche palm) is grown in Peru and Brazil for its edible fruit that is said to contain phytoestrogens, but the relevant estrogenic compounds have not been identified. We investigated the constituents of moriche palm fruit extract and evaluated their estrogenic ability.Materials and methods: Ethyl acetate fraction of dried moriche palm was purified by column chromatography and HPLC chromatography. To evaluate estrogenic activity, we performed [1] simulation of binding to the human estrogen receptor (ER), [2] investigation of the proliferative effect on MCF-7 cells, and [3] the estrogen-chemically activated luciferase gene expression (E-CALUX) assay.Results: Two hydroxypterocarpans were isolated including lespeflorin G8 (LF) and 8-hydroxyhomopterocarpan (8-HHP). The binding affinity of LF to ERa was higher than that of 8-HHP, with inhibition constants of 81.9 nM and 1.99 mM, respectively. However, LF and 8-HHP exhibited a similar proliferative effect on MCF-7 cells at 10 mM. The E-CALUX assay demonstrated that LF is a full ER agonist and 8-HHP is a partial agonist.Conclusion: LF was identified as a major estrogenic compound in the fruit of Mauritia flexuosa.Keywords: Mauritia flexuosa, moriche palm, lespeflorin G8, homopterocarpan, estrogenic activity, MCF-7, E-CALUX