A Gram-negative, strictly aerobic, non-motile, and rod-shaped bacterial strain designated UB-M7(T) was isolated from the intestine of a sea cucumber (Apostichopus japonicus) collected from Pohang in South Korea. Strain UB-M7(T) displayed optimal growth at 25 °C, pH 7.0-7.5, and with 2.0-3.0 % (w/v) NaCl. Phylogenetic analyses based on the 16S rRNA gene sequences showed that strain UB-M7(T) clustered with Phaeobacter arcticus DSM 23566(T), Phaeobacter inhibens DSM 16374(T), Phaeobacter gallaeciensis BS107(T), and Phaeobacter leonis 306(T), exhibiting 16S rRNA gene sequence similarity values of 96.8, 96.6, 96.4, and 96.2 %, respectively. Strain UB-M7(T) was found to exhibit the highest gyrB sequence similarity value of 80.6 % to the type strain of P. arcticus. The major respiratory quinone of strain UB-M7(T) was found to be ubiquinone 10 (Q-10). The major cellular fatty acids (>5 % of the total fatty acids) are summed features 8 (comprising C18:1 ω7c and/or C18:1 ω6c), 11-methyl C18:1 ω7c, and cyclo C19:0 ω8c. The DNA G+C content was found to be 58.5 mol% and DNA-DNA relatedness value with P. arcticus JCM 14644(T) was 17.2 ± 2.4 %. The major polar lipids of strain UB-M7(T) were identified as phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine; one phospholipid, and three other lipids remain unidentified. Based on its phenotypic, phylogenetic, and chemotaxonomic properties it is concluded that strain UB-M7(T) represents a novel species in the genus Phaeobacter, for which the name Phaeobacter marinintestinus sp. nov. is proposed. The type strain is UB-M7(T) (=KCCM 43045(T) = JCM 19926(T)).