Geosmin is a typical odorant in potable water sources, but this substance is hardly removed by conventional water treatment. In this study, a promising facultative anaerobic bacterial strain was successfully isolated from a bioreactor and exhibited a high biodegradation rate of geosmin. 16S rRNA sequencing and physiological analysis were performed. Results showed that this strain belongs to Gram-negative Xanthobacter flavus. To date, this is the only study to report the isolation and characterization of a facultative anaerobic bacterium from a bioreactor capable of biodegrading geosmin as the sole carbon source. As additional carbon source of X. flavus-YW, beef extract (0.5 g/L) may enhance the biodegradation of geosmin. At an initial concentration of 50 µg/L, 60% of geosmin was biodegraded after 2 d, and 71.3% of geosmin was biodegraded after 10 d. This study is important in basic research and application of the efficient removal of geosmin from potable water sources.