Two yellow-coloured, Gram-stain-negative, motile, and rod-shaped bacteria, designated strains R-10-10(T) and R-10-15 were isolated from oil-contaminated soil. Both strains were able to grow at 4-40 degrees C, pH 5.5-10.5, and 0-4% (w/v) NaCl concentration. These strains were taxonomically characterized by a polyphasic approach. Based on the 16S rRNA gene sequence analysis, both strains, R-10-10(T) and R-10-15, could be affiliated to the genus Brevundimonas and shared highest sequence similarity with Brevundimonas staleyi FWC43(T) (98.8%), Brevundimonas bullata TK0051(T) (98.6%), and Brevundimonas subvibrioides CB81(T) (98.3%). The pairwise sequence similarity between strains R-10-10(T) and R-10-15 was 99.9%. Both strains R-10-10(T) and R-10-15 contained phosphatidylglycerol, diphosphatidylglycerol, and four unidentified glycolipids as major polar lipids; ubiquinone-10 as sole respiratory quinone; and summed feature 8 (C-18:1 omega 7c and/or C-18:1 omega 6c), C-16:0, summed feature 3 (C-16:1 omega 7c and/or C-16:1 omega 6c), and C-18:1 omega 9c as major fatty acids. The genomic DNA G+C content values of strains R-10-10(T) and R-10-15 were 67.1 and 66.9 mol%, respectively. The DNA-DNA relatedness between R-10-10(T) and R-10-15 was higher than 70% but the values were less than 55% with closely related reference type strains. The morphological, physiological, chemotaxonomic, and phylogenetic data clearly distinguished strain R-10-10(T) from its closest phylogenetic neighbors. Thus, strain R-10-10(T) is considered to represent a novel species of the genus Brevundimonas, for which the name Brevundimonas mongoliensis sp. nov. is proposed. The type strain is R-10-10(T) (=KEMB 9005-696(T) = KACC 19387(T) = JCM 32172(T)), and strain R-10-15 is considered as an additional strain of the novel species.