Abstract <p><i>Clostridium butyricum</i> inhabits various anoxic environments, including soil and the human gut. Here, this common bacterium comes into contact with abundant plant-derived flavonoids. Metabolization of these bioactive polyphenols has been studied in recent years, particularly focusing on gut bacteria due to the proposed health-promoting properties of these dietary constituents. Based on an initial report in 1997 on eriodictyol degradation (Miyake et al. 1997, J Agric Food Chem, 45:3738–3742), the present study systematically investigated <i>C. butyricum</i> for its ability to convert a set of structurally diverse flavonoids. Incubation experiments revealed that <i>C. butyricum</i> deglycosylated flavonoid <i>O</i>-glucosides but only when glucose was absent. Moreover, aglycone members of flavone, flavanone, dihydrochalcone, and flavanonol subclasses were degraded. The C-ring cleavage of the flavanones, naringenin and eriodictyol, was stereospecific and finally resulted in formation of the corresponding hydroxyphenylpropionic acids. Stereospecific C-ring cleavage of the flavanonol taxifolin led to taxifolin dihydrochalcone. <i>C. butyricum</i> did neither cleave flavonols and isoflavones nor catalyze de-rhamnosylation, demethylation, or dehydroxylation of flavonoids. Genes encoding potential flavonoid-metabolizing enzymes were detected in the <i>C. butyricum</i> genome. Overall, these findings indicate that <i>C. butyricum</i> utilizes flavonoids as alternative substrates and, as observed for the dihydrochalcone phloretin, can eliminate growth-inhibiting flavonoids through degradation.</p> Key points <p><i>• Clostridium butyricum deglycosylated flavonoid O-glucosides.</i></p> <p><i>• Clostridium butyricum converted members of several flavonoid subclasses.</i></p> <p><i>• Potential flavonoid-metabolizing enzymes are encoded in the C. butyricum genome.</i></p>