We isolated a human intestinal bacterium, capable of cleaving the C-ring and dehydroxylating the B-ring of both (+)-catechin (2R,3S) and (−)-epicatechin (2R,3R). Although the strain was classified as Eggerthella (Eg.) lenta [named Eg. sp. CAT-1 (JF798636)] by 16S ribosomal RNA (rRNA) gene similarity, it was quite different in substrate specificity from a previously isolated strain, Eg. sp. SDG-2, which takes part in cleavage of the C-ring and dehydroxylation of the 3,4-dihydroxyphenyl moiety (B-ring) of (3R)-flavan-3-ol derivatives. On the other hand, both Eg. sp. CAT-1 and Eg. sp. SDG-2 showed the same substrate specificity against dehydroxylation of enantiomeric lignans, (+)- and (−)-dihydroxyenterodiol, and (+)- and (−)-dihydroxyenterolactone.