A novel Gram stain-negative, catalase- and oxidase-positive, strictly aerobic bacterium, designated strain H50T, was isolated from an amphioxus breeding zone in the coastal region of the Yellow Sea, China. Cells were observed to be ovoid or short rods, lacked flagella and were found to contain bacteriochlorophyll a. Poly-beta-hydroxybutyrate was found to be accumulated. The temperature range for growth was determined to be 0–37 °C (optimum 28–37 °C). The halotolerance range for growth is 1–15 % NaCl (optimum 2–7 %). The pH range for growth is 6.0–8.0 (optimum 7.0). The major fatty acids were identified as C18:1ω7c and C16:0. The following polar lipids were found to be present: diphosphatidylglycerol, phosphatidylglycerol and a lipid. The predominant respiratory quinone was determined to be Q-10. DNA G+C content was determined to be 57.7 mol%. Strain H50T exhibited the highest 16S rRNA gene sequence similarity to Pelagicola litoralis DSM 18290T (96.1 %), Roseovarius mucosus DSM 17069T (95.8 %) and Roseovarius tolerans DSM 11457T (95.7 %). In the phylogenetic trees, strain H50T was clustered with the genus Roseovarius but not Pelagicola. On the basis of phenotypic, chemotaxonomic and genotypic data, strain H50T is considered to represent a novel species in the genus Roseovarius, for which the name Roseovarius marisflavi sp. nov. is proposed. The type strain is H50T (=CGMCC 1.10799T=JCM 17553T).