A mesophilic, anaerobic, cellulolytic and xylanolytic strain, UasXn-3T, was isolated from anaerobic granular sludge in a mesophilic upflow anaerobic sludge blanket reactor, which was used to treat municipal sewage. The cells were Gram-stain-negative, non-motile, and non-spore-forming rods. The optimal temperature for growth was 37-40 °C and the optimal pH for growth was pH 6.5-7.0. Strain UasXn-3T could grow on several polysaccharides and sugars, including cellulose, cellobiose, xylan, xylose, glucose, fructose, arabinose, mannose, raffinose, trehalose and starch. The DNA G+C content was 44.4 mol%. On the basis of comparative 16S rRNA gene sequence analysis, strain UasXn-3T was identified as a member of the genus Bacteroides and most closely related to Bacteroides oleiciplenus, B. intestinalis, B. cellulosilyticus and B. graminisolvens (sequence similarities of 91.3-91.6%). Since the genetic and phenotypic properties suggest that strain UasXn-3T represents a novel species, we propose the name Bacteroides luti sp. nov. The type strain is UasXn-3T (=JCM 19020T=DSM 26991T).