A novel marine flavobacterial species, designated 3KA7-17T, was isolated from the hard coral Acropora formosa D. collected in Japan. The strain was pale-orange pigmented, Gram-stain negative, strictly aerobic, coccus shaped, and non-motile. Preliminary analysis based on the 16S rRNA gene sequence revealed an affiliation with the family Flavobacteriaceae of the phylum Bacteroidetes, and it had the greatest sequence similarity (96.0%) to Seonamhaeicola algicola Gy8T. The DNA G + C content was 34.3 mol%. MK-6 was the major menaquinone, with iso-C15:1 H and/or C13:0 3-OH (24.3%), iso-C15:0 (19.5%), iso-C15:0 3-OH (14.2%), and iso-C17:0 3-OH (15.9%) as the main (> 10%) cellular fatty acids. The major polar lipid profile consisted of phosphatidylethanolamine, two unidentified aminolipids, and two unidentified lipids. Based on distinct phylogenetic and phenotypic evidence, the strain represents a novel species of the genus Seonamhaeicola, for which the name Seonamhaeicola acroporae sp. nov. is proposed and the type strain is 3KA7-17T (= KCTC 62713T = NBRC 113410T).