Nine strains capable of metabolizing isoflavones to equol were isolated from human faeces. Four of the strains were characterized by determining phenotypic and biochemical features and their phylogenetic position based on 16S rRNA gene sequence analysis. These strains were related to Eggerthella sinensis HKU14T with about 93 % 16S rRNA gene sequence similarity; they were asaccharolytic, obligately anaerobic, non-spore-forming, non-motile and Gram-positive coccobacilli. In enzyme activity tests, arginine dihydrolase, arginine and leucine arylamidases were positive but nitrate reduction, urease and beta-glucosidase were negative. The major menaquinone was DMMK-6 (dimethylmenaquinone-6), while that of members of the genus Eggerthella was MMK-6 (methylmenaquinone-6). Furthermore, the cell-wall peptidoglycan type of these strains was A1gamma, while that of members of the genus Eggerthella was A4gamma. On the basis of these data, a new genus, Adlercreutzia gen. nov., is proposed with one species, Adlercreutzia equolifaciens sp. nov. The type strain of Adlercreutzia equolifaciens is FJC-B9T (=JCM 14793T =DSM 19450T =CCUG 54925T).