An aerobic, Gram-positive, non-motile, non-spore-forming, rod-coccus-shaped bacterium, strain 5317S-21(T), was isolated from an air sample from Suwon city, Republic of Korea. The isolate was able to grow within a pH range of 5.0-9.0 and a temperature range of 5-35 degrees C and it tolerated up to 2 % (w/v) NaCl. The cell-wall peptidoglycan contained meso-diaminopimelic acid as diagnostic diamino acid. The predominant isoprenoid quinone was MK-8(H(4)). The major polar lipids were phosphatidylinositol, phosphatidylethanolamine and diphosphatidylglycerol; phosphatidylglycerol and several unknown phospholipids were also detected. Mycolic acids were absent. The only whole-cell sugar was glucose. The major cellular fatty acids were iso-C(16 : 0), C(17 : 1)omega8c and iso-C(15 : 0). 16S rRNA gene sequence analysis indicated that strain 5317S-21(T) was related phylogenetically to members of the genus Knoellia, with 97.4 % sequence similarity to the type strains of Knoellia sinensis and Knoellia subterranea. The G+C content of the genomic DNA of strain 5317S-21(T) was 73 mol%. Levels of DNA-DNA relatedness between strain 5317S-21(T) and the type strains of Knoellia sinensis and Knoellia subterranea were 37 and 41 %, respectively. It was concluded that strain 5317S-21(T) represents a novel species of the genus Knoellia, for which the name Knoellia aerolata sp. nov. is proposed. The type strain is 5317S-21(T) (=KACC 20583(T) =DSM 18566(T)).