A novel actinobacterium, designated HIr16-25T, was isolated from the rhizosphere soil of a mangrove growing on Iriomote Island in Japan. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain HIr16-25T fell within the cluster of the members of the genus Agromyces and the highest sequence similarity value was observed with Agromyces rhizospherae IFO 16236T (98.6%). Strain HIr16-25T possessed l-2,4-diaminobutyric acid as a diagnostic diamino acid of the peptidoglycan, and MK-12 and MK-11 as the predominant menaquinones. The major fatty acids were identified as iso-C16:0, anteiso-C15:0 and anteiso-C17:0 and the principal polar lipids were phosphatidylglycerol and one glycolipid. These chemotaxonomic features matched well those described for the members of the genus Agromyces. Meanwhile, the result of DNA–DNA hybridization and the presence of differential phenotypic characteristics between strain HIr16-25T and the type strain of A. rhizospherae indicated that strain HIr16-25T be classified as a novel species of the genus Agromyces. Therefore, we propose strain HIr16-25T to represent a novel species of the genus Agromyces, with the name Agromyces mangrovi sp. nov. The type strain is HIr16-25T (= NBRC 112812T = TBRC 7760T).