We described the polyphasic characterization of the psychrotolerant isolated from Antarctic seawater. The strain was closely related to Flavobacterium hydatis, F. pectinovorum, and F. saccharophilum on the basis of the 16S rDNA sequence analysis. However, DNA-DNA hybridization experiments showed that the DNA-similarities between strain KUC-1T and the reference strains of Flavobacterium were less than 30%. Therefore, we can definite a new species of Flavobacterium phylogenetically, and strain KUC-1T can be considered to be a new species of Flavobacterium. i.e. F. frigidimaris (KUC-1T: JCM 12218T and DSM 15937T; mol% G+C of DNA of the type strain is 34.5 mol%). Useful phenotypical features for discrimination of F. frigidimaris from other Flavobacterium species, such as a resistance to NaCl, optimum growth temperature, and cellular fatty acid composition, were also determined.