A Gram-staining-negative, rod-shaped, non-spore-forming bacterium, designated strain RG4-7(T), was isolated from the moss Polytrichastrum formosum collected from Gawalong glacier in Tibet, China, and characterized by using a polyphasic taxonomic approach. The predominant fatty acids of strain RG4-7(T) were summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0 and iso-C17 : 0 3-OH. The major polar lipids were phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipid, two unidentified aminolipids and one unidentified lipid. Strain RG4-7(T) contained MK-7 as the dominant menaquinone and the G+C content of its genomic DNA was 39.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain RG4-7(T) was affiliated to species of the genus Mucilaginibacter, and its closest relative was Mucilaginibacter jinjuensis YC7004(T) (97.0 % sequence similarity). However, the DNA-DNA relatedness between this strain and strain RG4-7(T) was only 49.1±3.7 %. Based on phylogenetic inference and phenotypic data, strain RG4-7(T) is considered to represent a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter polytrichastri sp. nov. is proposed. The type strain is RG4-7(T) ( = CGMCC 1.12493(T) = DSM 26907(T)). An emended description of the genus Mucilaginibacter is also proposed.