A Gram-stain negative, facultatively anaerobic, non-motile and rod shaped bacterium, designated FA423(T), was isolated from a marine sediment obtained off the coast of Weihai, China. Strain FA423(T) was found to grow at 17-42 °C (optimum, 33 °C) and pH 5.5-8.0 (optimum, 7.0-7.5) in the presence of 0.5-6.0 % (w/v) NaCl (optimum, 1.0-2.0 %). Cells were found to be catalase positive and oxidase negative. Phylogenetic analysis of its 16S rRNA gene sequence revealed that strain FA423(T) is a member of the genus Mangrovibacterium and exhibits the highest sequence similarity (95.9 %) to the type strain of Mangrovibacterium diazotrophicum. The dominant cellular fatty acids were identified as summed feature 4 (iso-C17:1 I and/or anteiso-C17:1 B) and iso-C15:0. Menaquinone MK-7 was found to be the sole respiratory quinone. The major polar lipids were found to be an unidentified lipid and an unidentified phospholipid. The DNA G+C content of strain FA423(T) is 47.4 mol%. Based on the phylogenetic and phenotypic characteristics, strain FA423(T) is considered to represent a novel species of the genus Mangrovibacterium, for which the name Mangrovibacterium marinum sp. nov. is proposed. The type strain is FA423(T) (=DSM 28823(T) = KCTC 42253(T) = CICC 10903(T)).