A novel Gram-negative, non-motile bacterium, designated ZXM137(T), was isolated from seawater collected from a coastal region of Qingdao, China, during a massive green algae (Enteromorpha prolifera) bloom. Strain ZXM137(T) was strictly aerobic and did not accumulate poly-β-hydroxybutyrate. Growth occurred with 0.5-11.0% (w/v) NaCl, at pH 6-9 (optimum of pH 7) and at 4-45 °C (optimum at 28 °C). It contained Q-10 as the predominant ubiquinone and the major polar lipids were phosphatidylglycerol, phospholipids, and an unidentified aminolipid and lipid. The major cellular fatty acids of strain ZXM137(T) were C(18:1)ω7c, C(18:1)ω6c and 11-methyl C(18:1)ω7c. The DNA G+C content was 60.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain ZXM137(T) formed a distinct evolutionary lineage within the Roseobacter group in the class Alphaproteobacteria. On the basis of phenotypic, chemotaxonomic and phylogenetic evidence, strain ZXM137(T) represents a novel species in a new genus, for which the name Huaishuia halophila gen. nov., sp. nov. is proposed; the type strain is ZXM137(T) (=CGMCC 1.8891(T)=LMG 24854(T)).