In this study, the taxonomic position of an actinobacterium, strain YIM M 10931(T), which was isolated from a mangrove sediment sample collected in Dugong Creek, Little Andaman, India, was determined by a polyphasic approach. This gram-positive, aerobic strain produced branched substrate mycelium and aerial hyphae, which differentiated into short, hooked or spiral spore chains. The organism contained meso-diaminopimelic acid as the diagnostic diamino acid in the cell-wall peptidoglycan. The whole cell sugars consisted of mannose, ribose, glucose, galactose and madurose. The cellular fatty acid profile mainly consisted of iso-C(16 : 0), 10-methyl C(18 : 0) and C(16 : 0). The quinone system was predominantly composed of MK-9(H(8)) (45.5 %) and MK-9(H(6)) (39 %). The phospholipids detected were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol mannoside, phosphatidylinositol and two unknown phospholipids. The organism showed a combination of morphological and chemotaxonomic properties typical of members of the genus Actinomadura. Moreover, phylogenetic analysis based on a 16S rRNA gene sequence generated from the strain identified its closest relatives as Actinomadura cremea DSM 43676(T) (98.4 % sequence similarity), Actinomadura rifamycini DSM 43936(T) (97.4 %) and Actinomadura apis IM17-1(T) (96.9 %). It was obvious from the resulting phylogenetic trees that strain YIM M 10931(T) belongs to a distinct subclade within the evolutionary radiation of the genus Actinomadura. DNA-DNA hybridizations of strain YIM M 10931(T) with A. cremea DSM 43676(T) and A. rifamycini DSM 43936(T) were performed and further confirmed that the isolate represents a separate genomic species. Based on the phenotypic and genotypic characteristics presented, it is proposed that strain YIM M 10931(T) represents a novel species within the genus Actinomadura, for which the name Actinomadura sediminis sp. nov. is proposed; the type strain is YIM M 10931(T) ( = CCTCC AA 2010009(T) = DSM 45500(T)).