Two novel Gram-stain-positive actinobacteria, designated H23-8(T) and H23-19, were isolated from a sea sediment sample and their taxonomic positions were investigated by a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequence comparisons showed that these isolates were closely related to the members of the genus Agromyces, with similarity range of 94.5-97.4%. Strains H23-8(T) and H23-19 contained L-2,4-diaminobutyric acid, D-alanine, D-glutamic acid and glycine in their peptidoglycan. The predominant menaquinones were MK-13 and MK-12, and the major fatty acids were anteiso-C(15:0), anteiso-C(17:0) and iso-C(16:0). The DNA G+C content was 72.3-72.5 mol%. The chemotaxonomic characteristics of the isolates matched those described for members of the genus Agromyces. The results of phylogenetic analysis and DNA-DNA hybridization, along with differences in phenotypic characteristics between strains H23-8(T) and H23-19 and the species of the genus Agromyces with validly published names, indicated that the two isolates should be assigned to a novel species of the genus Agromyces, for which the name Agromyces marinus sp. nov. is proposed; the type strain is H23-8(T) (=NBRC 109019(T)=DSM 26151(T)).