A bacterium (named OT-1(T)) that showed algicidal activity was isolated from sea water of Masan Bay, Korea, during an outbreak of red tide. Phylogenetic analysis based on 16S rDNA sequences showed that the isolate formed a distinct phyletic lineage within the family Flavobacteriaceae of the Cytophaga-Flavobacterium-Bacteroides group. No species with a validly published name showed >/=93 % 16S rRNA gene sequence similarity to strain OT-1(T). The isolate had major amounts of iso-branched and 3-hydroxy iso-branched fatty acids and menaquinone 6 and a DNA G+C content of 34 mol%; these chemotaxonomic characters also supported the placement of the organism in the family Flavobacteriaceae. The strain was Gram-negative, yellow-pigmented, non-motile, non-gliding, flexirubin-negative, strictly aerobic, catalase-negative, oxidase-positive and halophilic. Na(+), Ca(2+) and Mg(2+) ions were obligately required for growth. The strain utilized various sugars as sole carbon sources and degraded gelatin, skimmed milk and starch. Several phenotypic characters can be used to differentiate the test strain from phylogenetically related marine bacterial genera. On the basis of polyphasic evidence, it is proposed that strain OT-1(T) should be assigned to the family Flavobacteriaceae as Kordia algicida gen. nov., sp. nov. The type strain is OT-1(T) (=KCTC 8814P(T)=NBRC 1000336(T)).