A Gram-negative, facultatively anaerobic, slightly halophilic bacterium that was motile by gliding, designated KMM 6390(T), was isolated from the coastal green alga Ulva fenestrata collected from the Sea of Japan. A comparative analysis of 16S rRNA gene sequences revealed that strain KMM 6390(T) was a member of the genus Winogradskyella, with Winogradskyella echinorum KMM 6211(T) as its closest relative (97.8% 16S rRNA gene sequence similarity). 16S rRNA gene sequence similarities between the isolate and other members of the genus Winogradskyella were 95.4-96.7%. DNA-DNA relatedness between the isolate and W. echinorum KMM 6211(T) was 27%. Strain KMM 6390(T) was able to grow with 0.5-4.0% NaCl and at 4-37 °C. The isolate decomposed casein, gelatin, starch and DNA and produced acid from galactose, D-glucose, lactose and maltose. The major fatty acids were iso-C(15:0), iso-C(15:1), anteiso-C(15:0) and C(15:0). The polar lipid profile comprised phosphatidylethanolamine and two unknown aminolipids. The DNA G+C content was 34.2 mol%. On the basis of phylogenetic, chemotaxonomic and phenotypic investigations, strain KMM 6390(T) represents a novel species of the genus Winogradskyella, for which the name Winogradskyella ulvae sp. nov. is proposed; the type strain is KMM 6390(T) (=KCTC 23626(T)=LMG 26444(T)). Emended descriptions of the genus Winogradskyella and of W. thalassocola, W. echinorum, W. exilis and W. eximia are also provided.