A Gram-stain-positive, non-motile and aerobic bacterium, designated strain DW151BT, was isolated from a sludge sample of a dairy industry effluent treatment plant. 16S rRNA gene sequence analysis of strain DW151BT placed it within the genus Rhodococcus. It displayed significant similarity with recognized species of the genus: Rhodococcus pyridinivorans PDB9T (98.8 %), Rhodococcus gordoniae W 4937T (98.6 %), Rhodococcus rhodochrous DSM 43241T (98.5 %) and Rhodococcus artemisiae YIM 65754T (97.5 %). However, strain DW151BT differed from phylogenetically closely related species in various phenotypic properties. The cellular polar lipid profile consisted of diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) as major lipids, MK-8(H2) was the major menaquinone and meso-diaminopimelic acid was the cell-wall peptidoglycan. The fatty acid profile consisted of C16 : 0, C18 : 1cis9 and C16 : 1cis9 as main components. The presence of C16 : 0 and diphosphatidylglycerol as major fatty acid and polar lipid, respectively, was in accordance with chemotaxonomic markers of the genus Rhodococcus. The DNA G+C content of strain DW151BT was 69.9 mol%, a value within the limits reported for the members of this genus. Furthermore, strain DW151BT showed low similarity at the whole genome level in DNA-DNA hybridization experiments with phylogenetically closely related strains. Considering the low similarity at the genome level and differences in phenotypic properties, strain DW151BT is considered to represent a novel species of the genus Rhodococcus, for which the name Rhodococcus lactis sp. nov. is proposed. The type strain is DW151BT ( = MTCC 12279T = DSM 45625T).