Theaflavin-3,3′-digallate　(TFDG),　a　bioactive　black　tea　phenolic,　is　poorly　absorbed　in　the　small　intestine,　and　it　has　been　suggested　that　gut　microbiota　metabolism　plays　a　crucial　role　in　its　bioactivities.　However,　information　on　its　metabolic　fate　and　impact　on　gut　microbiota　is　limited.　Here,　TFDG　was　anaerobically　fermented　in　vitro　by　human　fecal　microbiota,　and　epigallocatechin　gallate　(EGCG)　was　used　for　comparison.　Despite　the　similar　flavan-3-ol　skeletons,　TFDG　was　more　slowly　degraded　and　yielded　a　distinctively　different　metabolic　profile.　The　formation　of　theanaphthoquinone　as　the　main　metabolites　was　unique　to　TFDG.　Additionally,　a　number　of　hydroxylated　phenylcarboxylic　acids　were　formed　with　low　concentrations,　when　comparing　to　EGCG　metabolism.　Microbiome　profiling　demonstrated　several　similarities　in　gut　microbiota　modulatory　effects,　including　growth-promoting　effects　on　Bacteroides,　Faecalibacterium,　Parabacteroides,　and　Bifidobacterium,　and　inhibitory　effects　on　Prevotella　and　Fusobacterium.　In　conclusion,　TFDG　and　EGCG　underwent　significantly　different　microbial　metabolic　fates,　yet　their　gut　microbiota　modulatory　effects　were　similar.　©　2020　American　Chemical　Society.