A novel actinomycete, designated strain CS5-AC17(T), was isolated from cliff soil in the Republic of Korea. Cells of the organism were aerobic and catalase- and oxidase-negative. Substrate mycelium was well developed and was pale to strong yellow. Spore chains were borne on rudimentary aerial mycelium. The spores (0.4-0.5x0.9-1.6 microm) were smooth surfaced and cylindrical. Growth occurred at 25-42 degrees C, at pH 5.1-12.1 and in the presence of up to 4 % NaCl. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the isolate was closely related to members of the genus Actinocatenispora in the family Micromonosporaceae. The phylogenetic neighbours were Actinocatenispora thailandica TT2-10(T) (97.7 % 16S rRNA gene sequence similarity) and Actinocatenispora sera KV-744(T) (97.6 %). The diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The major respiratory quinones were MK-9(H(4)), MK-9(H(6)) and MK-9(H(8)). The polar lipids contained phosphatidylethanolamine and phosphatidylinositol with a small amount of phosphatidylglycerol. The DNA G+C content was 74.3 mol%. DNA-DNA relatedness values between strain CS5-AC17(T) and its phylogenetically closest relatives were 6.1-7.1 % (A. thailandica DSM 44816(T)) and 21.5-27.6 % (A. sera NRRL B-24477(T)). On the basis of the phenotypic features and the DNA-DNA hybridization data, strain CS5-AC17(T) (=DSM 45178(T)=NRRL B-24660(T)) represents a novel species of the genus Actinocatenispora, for which the name Actinocatenispora rupis sp. nov. is proposed.