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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).