A novel Gram-positive bacterium, strain 40(T), was isolated in the course of identifying bacteria from infective juveniles of the entomopathogenic nematode Steinernema thermophilum. Based on 16S rRNA gene analysis, strain 40(T) was found to be related to the type strains of recognized species of the genus Leucobacter, family Microbacteriaceae. The 16S rRNA gene sequence similarity values of strain 40(T) and Leucobacter albus IAM 14851(T), Leucobacter luti LMG 23118(T), Leucobacter alluvii LMG 23117(T), Leucobacter komagatae DSM 8803(T), Leucobacter chromiireducens CIP 108389(T) and Leucobacter aridicollis CIP 108388(T), respectively, were 97.3, 97.5, 97.6, 97.6, 97.6 and 98.5 %. Chemotaxonomic analysis also supported the affiliation of strain 40(T) to the genus Leucobacter: the major menaquinone was MK-11, the peptidoglycan cross-linkage was of the B-type, the cell wall diamino acid was L-diaminobutyric acid and the major fatty acids were anteiso-C(15 : 0) (42 %), anteiso-C(17 : 0) (34 %) and iso-C(16 : 0) (16 %). Based upon the biochemical and genomic analyses, strain 40(T) is sufficiently distinct from the type strains of recognized Leucobacter species to warrant the description of a novel species, for which the name Leucobacter iarius sp. nov. is proposed. The type strain is strain 40(T) (=DSM 17402(T)=CIP 108831(T)).