A Gram-stain negative, aerobic, motile and rod-shaped bacterial strain, designated J-MY2(T), was isolated from a tidal flat sediment of the South Sea, South Korea. Strain J-MY2(T) was found to grow optimally at 30 °C, at pH 7.0-8.0 and in the presence of 2.0 % (w/v) NaCl. Phylogenetic trees based on 16S rRNA gene sequences revealed that strain J-MY2(T) forms a cluster with the type strains of Simiduia species. Strain J-MY2(T) exhibited 16S rRNA gene sequence similarity values of 97.62-98.77 % to the type strains of four Simiduia species and of <92.95 % sequence similarity to the type strains of the other recognized species. Strain J-MY2(T) was found to contain Q-8 as the predominant ubiquinone and summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), C16:0, C18:1 ω7c and C17:1 ω8c as the major fatty acids. The major polar lipids of strain J-MY2(T) were identified as phosphatidylethanolamine, phosphatidylglycerol, three unidentified glycolipids and one unidentified lipid. The DNA G+C content of strain J-MY2(T) was determined to be 54.8 mol% and its mean DNA-DNA relatedness values with the type strains of the four Simiduia species were in the range 21-34 %. The differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that strain J-MY2(T) is separated from other Simiduia species. On the basis of the data presented, strain J-MY2(T) is considered to represent a novel species of the genus Simiduia, for which the name Simiduia aestuariiviva sp. nov. is proposed. The type strain is J-MY2(T) ( = KCTC 42073(T) = CECT 8571(T)).