Two marine bacterial strains designated Y2-1-60^T and GM1-28 were isolated from sediments of cordgrass and mangrove along the Luoyang estuary in Quanzhou Bay, China, respectively. Both strains were Gram-staining-negative, straight rod-shaped, non-flagellum, facultatively anaerobic, nitrogen-fixing, and did not contain carotenoid pigment. Catalase activities were found to be weak positive and oxidase activities negative. The 16S rRNA gene sequences of the two strains were identical and had maximum similarity of 98.0% with Maribellus luteus XSD2^T, and of <94.5% with other species. ANI value (96.9%) and DDH estimate (71.5%) between the two strains supported that they belonged to the same species. ANI value and DDH estimate between the two strains and M. luteus XSD2^T was 74.3% and 19.4%, respectively, indicating that they represent a novel species. Phylogenetic analysis based on 16S rRNA gene and phylogenomic analysis indicated that strains Y2-1-60^T and GM1-28 formed a monophyletic branch within the genus Maribellus. The respiratory quinone was menaquinone MK-7. The major fatty acid (>10%) consisted of iso-C_15:0, and iso-C_17:0 3-OH. The polar lipids consisted of phosphatidylethanolamine and several unidentified lipids. The genomic G + C contents were 41.9–42.0 mol%. Gene annotation revealed that strains Y2-1-60^T and GM1-28 contained a set of nif gene cluster (nifHDKENB) responsible for nitrogen fixation. Based on the above characteristics, strains Y2-1-60^T and GM1-28 represent a novel species within the genus Maribellus. Thus, Maribellus sediminis sp. nov. is proposed with type strain Y2-1-60^T (=MCCC 1K04285^T = KCTC 72884^T), isolated from cordgrass sediment and strain GM1-28 (=MCCC 1K04384 = KCTC 72880), isolated from mangrove sediment.