A Gram-staining-positive, white-coloured, aerobic, non-motile, catalase-positive and oxidase-negative, endophytic actinobacterium, designated strain EGI 6500322(T), was isolated from the surface-sterilized root of the halophyte Salsola affinis C. A. Mey collected from Urumqi, Xinjiang province, north-west China. Growth occurred at 5-35 °C (optimum 25-30 °C), at pH 5-10 (optimum pH 7-8) and with 0-13% NaCl (w/v) (optimum 0-5%). The predominant menaquinone was MK-9 (93.1%). The major cellular fatty acids were anteiso-C15:0 (49.5%) and iso-C15:0 (15.1%). The cell-wall peptidoglycan contained lysine, alanine and glutamic acid. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two unknown phospholipids and one unknown glycolipid. The DNA G+C content of strain EGI 6500322(T) was 62.0 mol%. Based on 16S rRNA gene sequence analysis, the nearest phylogenetic neighbours of strain EGI 6500322(T) were identified as Arthrobacter ardleyensis DSM 17432(T) (98.38%) and Arthrobacter bergerei DSM 16367(T (98.37%). The DNA-DNA relatedness between strain EGI 6500322(T) and Arthrobacter ardleyensis DSM 17432(T) and Arthrobacter bergerei DSM 16367(T) was 53.4 ± 4.1% and 30.5 ± 1.7%, respectively. On the basis of the phylogenetic analysis, chemotaxonomic data, physiological characteristics and DNA-DNA hybridization data, strain EGI 6500322(T) should represent a novel species of the genus Arthrobacter, for which the name Arthrobacter endophyticus sp. nov. is proposed. The type strain is EGI 6500322(T) ( = CTC 29490(T) = JCM 30091(T)).