The novel actinomycete, strain CH3-3T, was isolated from mangrove sediment collected from Chonburi Province, Thailand. On the basis of its spore morphology and chemotaxonomic characteristics, the strain belonged to the genus Micromonospora. It contained meso-diaminopimelic acid, glucose, mannose, xylose, ribose and rhamnose in the whole-cell hydrolysate, MK-10(H4), MK-10(H6) and MK-10(H8) as major menaquinones, and iso-C15 : 0, iso-C16 : 0 and iso-C17 : 0 as major cellular fatty acids. blast analysis of 16S rRNA gene sequences revealed that the strain showed highest similarity with Micromonospora palomenae NEAU-CX1T (98.97 %) and Micromonospora coxensis 2-30-b(28)T (98.97 %). Based on phylogenetic tree analysis of the 16S rRNA gene sequence, the strain formed a cluster with M. palomenae NEAU-CX1T, Micromonospora halophytica DSM 43171T, M. coxensis 2-30-b(28)T and Micromonospora purpureochromogenes DSM 43821T. On the basis of phenotypic differences and DNA-DNA relatedness evidence, strain CH3-3T could be clearly distinguished from the closely related species of the genus Micromonospora and represents a novel species of the genus Micromonospora for which the name Micromonospora sediminis sp. nov. is proposed. The type strain is CH3-3T (=JCM 18523T=PCU 350T=TISTR 2396T).