A Gram-stain-negative, aerobic, non-spore-forming, non-flagellated and rod-shaped or ovoid bacterial strain, designated BG-MY13(T), was isolated from a tidal flat sediment on the South Sea, South Korea. Strain BG-MY13(T) grew optimally at 30-35 °C, at pH 7.0-8.0 and in the presence of 2.0-3.0% (w/v) NaCl. Phylogenetic trees based on 16S rRNA gene sequences revealed that strain BG-MY13(T) falls within the cluster comprising the type strains of species of the genus Gramella . Strain BG-MY13(T) exhibited 16S rRNA gene sequ4ence similarity values of 96.9-97.8% to the type strains of Gramella echinicola , Gramella gaetbulicola , Gramella portivictoriae and Gramella marina and of 94.6-96.5% to the type strains of other species of the genus Gramella with validly published names. Strain BG-MY13(T) contained MK-6 as the predominant menaquinone and iso-C(15 : 0) and iso-C(17 : 0) 3-OH as the major fatty acids. The major polar lipids were phosphatidylethanolamine and one unidentified lipid. The DNA G+C content of strain BG-MY13(T) was 38.9 mol% and DNA-DNA relatedness values with the type strains of G. echinicola , G. gaetbulicola , G. portivictoriae and G. marina were 12-23%. The differential phenotypic properties, together with phylogenetic and genetic distinctiveness, revealed that strain BG-MY13(T) is separated from other species of the genus Gramella . On the basis of the data presented, strain BG-MY13(T) is considered to represent a novel species of the genus Gramella , for which the name Gramella aestuariivivens sp. nov. is proposed. The type strain is BG-MY13(T) ( = KCTC 42285(T) = NBRC 110677(T)).