A Gram-stain-negative, motile, facultative anaerobic and rod-shaped bacterium, designated strain NR704-98T, was isolated from marine sediment of the northern South China Sea. Cells were positive for oxidase and catalase activity. Growth was observed at 4–30 °C (optimum 20–25 °C), at pH 6–9 (pH 7) and with 0.5–7 % NaCl (2 %). The 16S rRNA gene-based phylogenetic analysis revealed that the nearest phylogenetic neighbours of strain NR704-98T were Shewanella woodyi MS32T (97.9 %), Shewanella hanedai 281T (97.1 %), Shewanella sediminis HAW-EB3T (96.8 %) and Shewanella canadensis HAW-EB2T (96.7 %). Based on the results of phylogenomic analysis, the average nucleotide identity and the digital DNA–DNA hybridization values between strain NR704-98T and the previously mentioned type strains of species of the genus Shewanella were in the range of 74.9–93.1 % and 20.6–51.4 %, respectively. The respiratory quinones were Q-7 and Q-8. The predominant fatty acids (>10 %) of strain NR704-98T were C16 : 0, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and iso-C15 : 0. Phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminophospholipids and five unidentified lipids were detected in strain NR704-98T. Based on the phylogenetic and phenotypic characteristics, strain NR704-98T is considered to represent a novel species of the genus Shewanella , for which the name Shewanella nanhaiensis sp. nov. is proposed. The type strain is NR704-98T (=KCTC 82799T=MCCC 1K06091T).