Strain T258T was isolated from forest soil at Bongnae Falls, South Korea. The strain exhibited antimicrobial and antifungal activity against the following strains: Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Paenibacillus larvae, Escherichia coli, Candida albicans and Aspergillus niger. Growth occurred on all ISP media tested (2, 3, 4, 5, 6 and 7), Czapek-Dox agar, potato dextrose agar, trypticase soy agar, Bennett's modified agar and nutrient agar at 28 °C. Aerial spores were produced solely on ISP Medium 4; the colour of the aerial mycelium was white and the substrate mycelium was ivory. Melanin production was negative on peptone-yeast extract iron agar (ISP Medium 6). The cell-wall peptidoglycan contained ll-diaminopimelic acid, glutamic acid, alanine and glycine. Whole-cell hydrolysates contained glucose, ribose and galactose. The predominant menaquinones were MK-9(H6) and MK-9(H8) while the minor menaquinone was MK-10(H2). The polar lipids included diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The major fatty acids (>10%) were C16 : 0 (29.8%), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) (15.1%), anteiso-C15 : 0 (13.5%) and iso-C15 : 0 (10.3%). DNA-DNA similarity with other strains ranged between 37.84 ± 1.15% and 50.25 ± 1.91 %. On the basis of these data, we suggest that strain T258T represents a novel species that belong to the genus Streptomyces, for which we propose a name Streptomyces polymachus sp. nov. The type strain is T258T ( = KACC 18247T = KEMB 9005-212T = NBRC 110905T).