A Gram-negative, non-motile, aerobic bacterium, designated strain IP7T, was isolated from seawater at the shore of the Incheon Eulwang-ri beach, South Korea. Cells of strain IP7T are straight or slightly rod-shaped and colonies are round, convex and orange-yellow. Strain IP7T is flexirubin-negative, mild halophile, catalase-and oxidase-positive, and produces a yellow-orange carotenoid pigment. Growth is optimal at 30°C, pH 7-9, and 2.0-4.0% NaCl (w/v). On the basis of 16S rRNA gene sequence similarity, strain IP7T is affiliated with genus Aestuariibaculum in the family Flavobacteriaceae, the closest relative being Aestuariibaculum suncheonense SC17T (98.3% sequence similarity). The DNA G + C content of the novel strain is 37.4 mol%. The only quinone is MK-6 menaquinone. Iso-branched C15:0, iso-branched C15:1 G, and iso-branched C17:0 3-OH are major fatty acids. The major polar lipids are phosphatidylethanolamine, an unidentified aminoglycolipid and two unidentified glycolipids. The DNA-DNA hybridization value of strain IP7T with Aestuariibaculum suncheonense SC17T is 28.87%. Based on the collective DNA-DNA hybridization, biochemical, phylogenetic and physiological data, we report a novel species of the genus Aestuariibaculum for which the name Aestuariibaculum marinum sp. nov. is proposed. The type strain is IP7T (= KCTC 52521T = JCM 31725T).