Three strains (KS8, KS9T and KS21), isolated from air samples near a composting facility, were subjected to taxonomic analyses (characterized using a polyphasic approach). Morphological and chemotaxonomic characteristics of the isolates were in agreement with those described for members of the genus Nocardiopsis. On the basis of 16S rRNA sequence comparison and phenotypic tests, KS21 clearly belonged to Nocardiopsis alba. KS8 and KS9T showed less than 98% 16S rRNA gene sequence similarity to any of the previously described Nocardiopsis species. The polar lipid profiles of both isolates consisted of four major compounds, phosphatidylmonomethylethanolamine, phosphatidylcholine, diphosphatidylglycerol and phosphatidylglycerol, in addition to two unknown phospholipids. The major menaquinones in KS8 and KS9T were MK-10(H8), MK-11(H8), MK-10(H6) and MK-12. Furthermore, MK-13, MK-11(H6), MK-9(H8) and MK-10(H4) could be detected in significant amounts. The fatty acid composition included iso- and anteiso-branched acids combined with tuberculostearic acid (Me18:0), straight-chain saturated (16:0, 18:0) and unsaturated (16:1, 17:1, 18:1) fatty acids. On the basis of these results, KS8 and KS9T clearly represent a novel species of the genus Nocardiopsis, for which the name Nocardiopsis compostus sp. nov. is proposed (type strain KS9T = DSM 44551T= NRRL B-24145T).