Strain $B31^T$ is a Gram-staining-negative, motile, and extremely halophilic archaeon that was isolated from salt-fermented seafood. Its morphology, physiology, biochemical features, and 16S rRNA gene sequence were determined. Phylogenetic analysis of its 16S rRNA gene sequence and composition of its major polar lipids placed this archaeon in the genus Halorubrum of the family Halobacteriaceae. Strain $B31^T$ showed 97.3, 97.2, and 96.9% 16S rRNA similarity to the type strains of Halorubrum alkaliphilum, Hrr. tibetense, and Hrr. vacuolatum, respectively. Its major polar lipids were phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me) and sulfated diglycosyl diether (S-DGD). Genomic DNA from strain $B31^T$ has a 61.7 mol % G+C content. Analysis of 16S rRNA gene sequences, as well as physiological and biochemical tests, identified genotypic and phenotypic differences between strain $B31^T$ and other Halorubrum species. The type strain of the novel species is $B31^T$ (=JCM $15757^T$ =DSM $19504^T$).