A Gram-negative, non-spore-forming, aerobic, motile and rod-shaped or ovoid bacterial strain, designated MA1-3(T), was isolated from a sea squirt (Halocynthia roretzi) collected from the South sea in South Korea. Strain MA1-3(T) was found to grow optimally at 25 °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 MA1-3(T) fell within the clade comprising Colwellia species, clustering coherently with the type strains of Colwellia aestuarii, Colwellia polaris and Colwellia chukchiensis, showing sequence similarity values of 97.2, 96.4 and 95.6 %, respectively. It exhibited 16S rRNA gene sequence similarity values of 93.9-96.1 % to the type strains of the other Colwellia species. Strain MA1-3(T) was found to contain Q-8 as the predominant ubiquinone and C16:1 ω7c and/or C16:1 ω6c, C16:0 and C16:1 ω9c as the major fatty acids. The DNA G+C content of strain MA1-3(T) was determined to be 39.1 mol% and its mean DNA-DNA relatedness value with the type strain of C. aestuarii was 13 ± 5.4 %. The differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that the novel strain is separated from other Colwellia species. On the basis of the data presented, strain MA1-3(T) is considered to represent a novel species of the genus Colwellia, for which the name Colwellia meonggei sp. nov. is proposed. The type strain is MA1-3(T) (=KCTC 32380(T) = CECT 8302(T)).