A thermophilic bacterium, designated DX-1T, was isolated from the anode biofilm of a microbial fuel cell (MFC). Cells of strain DX-1T were oxidase-positive, catalase-positive and Gram-staining-negative. The strain was found to be rod-shaped and non-motile and to produce subterminal spores. The strain was able to grow with NaCl at concentrations ranging from 0 to 6 %, at temperatures of 25-60 °C (optimum 55 °C) and pH 6.0-8.0 (optimum pH 7.0). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain DX-1T formed a cluster with Ureibacillus thermosphaericus DSM 10633T (96.9% 16S rRNA sequence similarity), Ureibacillus composti DSM 17951T (95.8%), Ureibacillus thermophilus DSM 17952T (95.7%) and Ureibacillus terrenus DSM 12654T (95.3%). The G+C content of the genomic DNA was 40.4 mol%. The major quinone was MK-7, the peptidoglycan type was L-Lys←D-Asp, and the major cellular fatty acids (>5%) were iso-C16:0 and iso-C14:0. The polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol and phospholipids of unknown composition. Based on phenotypic characteristics, chemotaxonomic features and results of phylogenetic analyses, the strain was determined to represent a distinct novel species of the genus Ureibacillus, and the name proposed for the novel species is Ureibacillus defluvii sp. nov., with type strain DX-1T (=CGMCC 1.12358T=KCTC 33127T).