A novel aerobic actinobacterium, strain EUM 273 ^T, was isolated from the root of a Grey Box tree (Eucalyptus microcarpa Maiden). Cells were Gram-staining-positive with well-developed substrate mycelia which were non-motile and rod-like, with coccoid elements. Phylogenetic evaluation based on 16S rRNA gene sequence analysis placed the isolate as a member of the family Promicromonosporaceae that was most closely related to Promicromonospora xylanilytica YIM 61515 ^T (98.2 %) and Promicromonospora vindobonensis V45 ^T (98 %). Chemotaxonomic data including cell wall components, major menaquinone and major fatty acids confirmed the affiliation of strain EUM 273 ^T to the genus Promicromonospora. The results of the phylogenetic analysis, including physiological and biochemical studies in combination with DNA-DNA hybridization, allowed the genotypic and phenotypic differentiation of strain EUM 273 ^T from the closest related species with validly published names. The name proposed for the novel species is Promicromonospora endophytica sp. nov. The type strain is EUM 273 ^T (=DSM 23716 ^T=NRRL B-24816 ^T). © 2012 IUMS.