A Gram-stain-negative, strictly aerobic and halotolerant bacterial strain, designated strain NAP41T, was isolated from a sea tidal flat in the Yellow Sea of South Korea. Cells were non-motile cocci showing oxidase- and catalase-positive activities. Growth of strain NAP41T was observed at 15-40 °C (optimum, 37 °C), at pH 6.5-9.0 (optimum, pH 7.0-7.5) and in the presence of 0.5-12 % (w/v) NaCl (optimum, 2 %). Strain NAP41T contained summed feature 8 (comprising C18 : ω7c/C18 : 1ω6c) and C18 : 0 as the major fatty acids and ubiquinone-10 as the sole isoprenoid quinone. Phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, an unidentified aminolipid and three unidentified lipids were detected as the polar lipids. The G+C content of the genomic DNA was 56.0 mol%. Strain NAP41T was most closely related to Primorskyibacter insulae SSK3-2T, Thalassococcus lentus YCS-24T and Roseivivax lentus DSM 29430T with 96.67, 96.39 and 96.39 % 16S rRNA gene sequence similarities, respectively, and formed a phylogenetic lineage distinct from closely related taxa within the family Rhodobacteraceae with low bootstrap values. On the basis of phenotypic, chemotaxonomic and molecular properties, strain NAP41T represents a novel species of a novel genus of the family Rhodobacteraceae, for whichthe name Aestuariicoccus marinus gen. nov., sp. nov. is proposed. The type strain of the type species is NAP41T (KACC 18431T=JCM 30739T).