Isoflavones (mainly daidzein and genistin) belong to the flavonoid group of compounds and are classified as phytoestrogens. In the intestine, daidzin is converted to daidzein by P-glucosidase, and then daidzein is converted to O-desmethylangolensin (O-DMA) or equol via dihydrodaidzein by enzymes of intestinal bacteria. We isolated, for the first time, an anaerobic gram-positive rod-shaped strain capable of producing equol from daidzein. Its 16S rDNA gene sequence (1428 bp) showed 99% similarity with that of the human intestinal bacterium SNU-Julong 732 (AY310748) and 93% similarity with that of Eggerthella lenta ATCC 25559(T) (AF292375). This strain converted daidzein to equol via dihydrodaidzein in an equol-assay medium anaerobically. The addition of butyric acid and arginine increased the conversion ratio of daidzein to equol 4.7- and 4.5-fold, respectively.