Two actinomycete strains, JSM1-1(T) and JSM1-3, were isolated from sea sand collected in Thailand. Their taxonomic position was determined using a polyphasic approach. The chemotaxonomic characteristics of these strains coincided with those of the genus Micromonospora, i.e. the presence of meso-diaminopimelic acid and N-glycolyl muramic acid in the peptidoglycan, whole cell sugar pattern D, phospholipids type II, and cellular fatty acid type 3b. Phylogenetic analysis of 16S rRNA gene sequences revealed a close relationship between strains JSM1-1(T) and JSM1-3 (99.8%), and between JSM1-1(T) and Micromonospora aurantiaca JCM 10878(T) (99.3%), Micromonospora chalcea JCM 3031(T) (99.0 %), and Micromonospora coxensis JCM 13248(T) (99.0%). However, strains JSM1-1(T) and JSM1-3 could be clearly distinguished from these type strains by a low DNA-DNA relatedness and by phenotypic differences. On the basis of the data presented, a new species, Micromonospora marina sp. nov., is proposed. The type strain is JSM1-1(T) (= JCM 12870(T) = PCU 269(T) = TISTR 1566(T)).