A Gram-staining-negative, non-spore-forming, facultatively aerobic, non-motile, rod-shaped bacterial strain, BR-3(T), was isolated from a tidal flat on the western coast of Korea, and subjected to a polyphasic study. Strain BR-3(T) grew optimally at 25 °C, at pH 6.5-7.0 and in the absence of NaCl. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain BR-3(T) fell within the clade comprising species of the genus Mucilaginibacter, joining the type strain of Mucilaginibacter rigui, with which it exhibited highest 16S rRNA gene sequence similarity (98.2%). 16S rRNA gene sequence similarity values between strain BR-3(T) and the type strains of the other species of the genus Mucilaginibacter were in the range 93.8-95.9%. A mean DNA-DNA relatedness value between strain BR-3(T) and M. rigui KCTC 12534(T) was 21%. Strain BR-3(T) contained MK-7 as the predominant menaquinone and C(16:1)ω7c and/or iso-C(15:0) 2-OH and iso-C(15:0) as the major fatty acids. The major polar lipids were phosphatidylethanolamine and an unidentified aminophospholipid. The DNA G+C content was 49.8 mol%. Differential phenotypic properties and phylogenetic and genetic distinctiveness of strain BR-3(T) demonstrated that this strain is separate from M. rigui as well as the other species of the genus Mucilaginibacter. On the basis of the data presented, strain BR-3(T) is considered to represent a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter lutimaris sp. nov. is proposed. The type strain is BR-3(T) (=KCTC 23461(T) =CCUG 60742(T)).