A Gram-negative, oxidase- and catalase-positive, rod-shaped, non-spore-forming, motile, aerobic bacterium, designated Y2^T, was isolated from surface seawater of Yundang Lake, Xiamen, China. The strain was able to grow in the presence of 0.5–6.0 % NaCl (optimum 1.0–1.5 %), at pH 5–10 (optimum pH 8) and at 10–40 °C (optimum 25 °C). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain Y2^T belongs to the genus Pseudoalteromonas , with the highest sequence similarity of 94.9 % to Pseudoalteromonas tunicata D2^T; within the genus Pseudoalteromonas , it showed the lowest similarity of 92.8 % to Pseudoalteromonas denitrificans ATCC 43337^T. The G+C content of the chromosomal DNA of strain Y2^T was 45.1 mol%. The predominant fatty acids were summed feature 3 (C_{16 : 1}ω6c and/or C_{16 : 1}ω7c), C_{16 : 0}, C_{12 : 0} 3-OH and summed feature 8 (C_{18 : 1}ω6c and/or C_{18 : 1}ω7c). The only respiratory quinone detected was Q-8. Based on the phylogenetic and phenotypic characteristics, strain Y2^T represents a novel species of the genus Pseudoalteromonas , for which the name Pseudoalteromonas xiamenensis sp. nov. is proposed; the type strain is Y2^T ( = CGMCC 1.12157^T = JCM 18779^T).