A novel exopolysaccharide-producing bacterium, designated strain SE3(T), was isolated from Pacific Ocean sediment. The strain was Gram-stain-negative, motile, strictly aerobic, oxidase-positive and catalase-positive, and required Na(+) for growth. Its major isoprenoid quinone was ubiquinone-8 (Q-8), and its cellular fatty acid profile mainly consisted of C16 : 1ω7c, C16 : 0 and C18 : 1ω7c. The DNA G+C content was 46.9 mol%. 16S rRNA gene sequence analysis suggested that strain SE3(T) is a member of the genus Pseudoalteromonas. Strain SE3(T) exhibited close phylogenetic affinity to Pseudoalteromonas arabiensis JCM 17292(T) (99.0 % 16S rRNA gene sequence similarity), Pseudoalteromonas lipolytica LMEB 39(T) (98.39 %) and Pseudoalteromonas donghaensis HJ51(T) (97.65 %). The DNA-DNA reassociation values between strain SE3(T) and P. arabiensis JCM 17292(T), P. lipolytica JCM 15903(T) and P. donghaensis LMG 24469(T) were 31, 26 and 44 %, respectively. Owing to the significant differences in phenotypic and chemotaxonomic characteristics, phylogenetic analysis based on 16S rRNA gene sequences and DNA-DNA relatedness data, the new isolate merits classification as a representative of novel species, for which the name Pseudoalteromonas shioyasakiensis is proposed. The type strain is SE3(T) ( = JCM 18891(T) = NCIMB 14852(T)).