A novel Gram-stain-positive actinobacterium, designated HT7-17T, was isolated from a sediment sample collected from the estuary of the Tama River, Japan, and its taxonomic position was investigated using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain HT7-17T was closely related to members of the genus Lysinimicrobium, with a similarity range of 97.1-98.2 %. The peptidoglycan type of strain HT7-17T was A4α, the predominant menaquinone was demethylmenaquinone DMK-9(H4) and the major fatty acids were anteiso-C15 : 0, C16 : 0 and iso-C16 : 0. The DNA G+C content was 69.9 mol%. These chemotaxonomic features corresponded to those of the genus Lysinimicrobium. Meanwhile, the differences in some phenotypic characteristics, along with the result of DNA-DNA hybridization, indicated that strain HT7-17T should be distinguished from the recognized species of the genus Lysinimicrobium. Therefore, strain HT7-17T represents a novel species of the genus Lysinimicrobium, for which the name Lysinimicrobium sediminis sp. nov. is proposed. The type strain is HT7-17T (=NBRC 112286T=TBRC 7037T).