A novel xylan-degrading bacterium, S3-E(T), was isolated from the biofilm of a membrane bioreactor. The cells of this strain were Gram-positive, non-motile, non-spore-forming rods, produced primary branches and formed yellow colonies on nutrient agar. The strain had chemotaxonomic markers that were consistent with classification in the genus Microbacterium, i.e. MK-12, MK-11 and MK-13 as the major menaquinones, predominant iso- and anteiso-branched cellular fatty acids, glucose and galactose as the cell-wall sugars, peptidoglycan-type B2beta with glycolyl residues and a DNA G+C content of 69.7 mol%. Phylogenetic analysis, based on 16S rRNA gene sequencing, showed that strain S3-E(T) is most similar to Microbacterium hominis IFO 15708(T) and Microbacterium foliorum DSM 12966(T) (97.6 and 97.4% sequence similarity, respectively), and that it forms a separate lineage with M. hominis in the genus Microbacterium. DNA-DNA hybridization results and phenotypic properties showed that strain S3-E(T) could be distinguished from all known Microbacterium species and represented a novel species, for which the name Microbacterium xylanilyticum sp. nov. is proposed; the type strain is S3-E(T) (=DSM 16914(T)=KCTC 19079(T)).