A bacterial strain, designated Y40(T), was isolated from sandy soil sampled on the Qinghai-Tibet Plateau. A polyphasic study confirmed the affiliation of the strain with the genus Mesobacillus. Strain Y40(T) was found to be an aerobic, Gram-stain-positive, motile and rod-shaped bacterium. The strain grew at 10-42 degrees C, pH 6-9 and with 0-2 % (w/v) NaCl. The diagnostic amino acid was meso-diaminopimeilic acid. MK7 was predominant menaquinone, and iso-C-15:0, iso-C-17:1 omega 10c and anteiso-C-15:0 were the major fatty acids. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified lipid. The DNA G+C content was 40.6 mol%. Based on he results of 16S rRNA gene sequence analysis, strain Y40(T) was phylogenetically closely related to Mesobacillus zeae JJ-247(T) and Mesobacillus foraminis CV53(T), with similarities of 98.0 and 97.7 %, respectively. The average nucleotide identity (ANIb) values between strain Y40(T) and Mesobacillus zeae JJ-247(T) and Mesobacillus foraminis CV53(T) were 69.9 and 70.0%, respectively. Based on the morphological, physiological, and chemotaxonomic data, it is proposed that strain Y40(T) (=CICC 24459(T)=JCM 32794(T)) should be classified into the genus Mesobacillus as Mesobacillus harenae sp. nov.