A novel actinomycete strain, designated CW 108(T), was isolated from a forest soil in Anhui Province, China. The cells were strictly aerobic, non-motile, bent rods. The strain grew optimally at 30-37 degrees C and pH 6.0-8.0. Chemotaxonomically, the peptidoglycan type was A3alpha, the cell-wall sugars contained galactose, mannose and ribose, the polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and phosphatidylmonomethylethanolamine, the major fatty acids were ai-C(15 : 0), i-C(15 : 0) and ai-C(17 : 0) and the predominant respiratory quinone was MK-9(H(2)), with a moderate amount of MK-8(H(2)) and a minor amount of MK-6(H(2)). The G+C content of the genomic DNA was 71.1 mol%. Phylogenetic analysis showed that strain CW 108(T) formed a deeply separated lineage in the family Micrococcaceae with Arthrobacter atrocyaneus DSM 20127(T). The 16S rRNA gene sequence similarity between strain CW 108(T) and Arthrobacter atrocyaneus DSM 20127(T) was 99.4 %; sequence similarities between these strains and representatives of other species in the family Micrococcaceae with validly published names were lower than 95.2 %. DNA-DNA hybridization showed a level of relatedness of 52.2 % between the two neighbours. Based on the results of our polyphasic taxonomic study, strain CW 108(T) and Arthrobacter atrocyaneus DSM 20127(T) should be assigned to two different species of a novel genus within the family Micrococcaceae, for which the names Sinomonas flava gen. nov., sp. nov. and Sinomonas atrocyanea comb. nov. are proposed. The type strain of Sinomonas flava is CW 108(T) (=LMG 24447(T) =KCTC 19388(T) =CCTCC AB 207194(T)) and the type strain of Sinomonas atrocyanea is DSM 20127(T) =JCM 1329(T) =CGMCC 1.1891(T) =ATCC 13752(T).