A novel Gram-stain-negative, rod-to-spiral-shaped, oxidase- and catalase- positive and facultatively aerobic bacterium, designated HS6(T), was isolated from marine sediment of Yellow Sea, China. It can reduce nitrate to nitrite and grow well in marine broth 2216 (MB, Hope Biol-Technology Co., Ltd) with an optimal temperature for growth of 30-33 °C (range 12-45 °C) and in the presence of 2-3% (w/v) NaCl (range 0.5-7%, w/v). The pH range for growth was pH 6.2-9.0, with an optimum at 6.5-7.0. Phylogenetic analysis based on 16S rRNA gene sequences demonstrated that the novel isolate was 93.3% similar to the type strain of Neptunomonas antarctica, 93.2% to Neptunomonas japonicum and 93.1% to Marinobacterium rhizophilum, the closest cultivated relatives. The polar lipid profile of the novel strain consisted of phosphatidylethanolamine, phosphatidylglycerol and some other unknown lipids. Major cellular fatty acids were summed feature 3 (C(16:1) ω7c/iso-C15:0 2-OH), C(18:1) ω7c and C(16:0) and the main respiratory quinone was Q-8. The DNA G+C content of strain HS6(T) was 61.2 mol%. Based on the phylogenetic, physiological and biochemical characteristics, strain HS6(T) represents a novel genus and species and the name Motiliproteus sediminis gen. nov., sp. nov., is proposed. The type strain is HS6(T) (=ATCC BAA-2613(T)=CICC 10858(T)).