A Gram-negative, rod-shaped, non-spore-forming aerobic bacterium, motile with a single polar flagellum, strain JLT2005(T), was isolated from surface seawater collected from the East China Sea and formed ivory white colonies on a rich organic medium. The strain was positive for catalase, oxidase, and urease. It grew in the presence of 0-12 % (w/v) NaCl (optimum 5 %), at 20-35 A degrees C (optimum 25 A degrees C), or at pH 6-10 (optimum pH 9). The major fatty acids (> 10 %) were C-18:1 omega 7c, C-19:0 omega 8c cyclo, C-16:0, and C-18:0. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, and five unidentified glycolipids. Ubiquinone-10 and Ubiquinone-11 were present as the major quinones. The DNA G+C content was 74.3 mol%. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain JLT2005(T) belongs to the genus Pelagibacterium in the family Hyphomicrobiaceae, class Alphaproteobacteria. The closest neighbors were Pelagibacterium halotolerans B2(T) (98.7 % similarity) and Pelagibacterium luteolum 1_C16_27(T) (97.1 % similarity). DNA-DNA relatedness values of strain JLT2005(T) with P. halotolerans B2(T) and with P. luteolum 1_C16_27(T) were 31.6 and 25 %. Evidence from genotypic, chemotaxonomic, and phenotypic data shows that strain JLT2005(T) represents a novel species of the genus Pelagibacterium, for which the name Pelagibacterium nitratireducens sp. nov is proposed. The type strain is JLT2005(T) (=CGMCC 1.10829(T) =JCM 17767(T)).