Three Gram-negative, aerobic, halophilic bacterial strains, SCM2-10 T , SCM-4, and 14C-6, were isolated from the algal medium of the red alga Pyropia yezoensis (previously classified as Porphyra yezoensis ) grown in laboratory experiments. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the organisms with high similarities to the three isolates are Sulfitobacter geojensis MM-124 T (98.7 %), Sulfitobacter noctilucicola NB-77 T (98.7 %), Sulfitobacter noctilucae NB-68 T (98.6 %), Sulfitobacter mediterraneus CH-B427 T (97.6 %), and Sulfitobacter porphyrae SCM-1 T (97.6 %), and that the three isolates belong to the genus Sulfitobacter , within the class Alphaproteobacteria . The DNA G+C contents of the three isolates were found to be in the range of 56.5–57.1 mol%. DNA–DNA hybridization experiments demonstrated that the genomic relatedness between strain SCM2-10 T and type strains of other Sulfitobacter species was in the range of 6.2–27.1 %. The predominant respiratory quinone of the three isolates was identified as ubiquinone-10. The dominant polar lipids in the three isolates were found to be phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and an unidentified amino lipid. The major fatty acid in the three isolates is C 18:1 ω 7 c . Strain SCM2-10 T demonstrated unique phenotypic characteristics, which differed from those of type strains of other Sulfitobacter species. Based on the phylogenetic, genetic, phenotypic, and chemotaxonomic data, we propose a novel species of the genus Sulfitobacter , which we named as Sulfitobacter pacificus sp. nov. The type strain of this species is strain SCM2-10 T (=LMG 27113 T = NBRC 109915 T ).