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ABSTRACT We evaluated the difference between rumen bacteria in Tan sheep fed either by grazing or in a feedlot. The aim was to provide a theoretical basis for ruminant nutrition and meat quality based on rumen fermentation. Twenty-four three-month-old Tan sheep were randomly and equally divided into two groups, the grazing group and ration group. Five sheep of each group were selected for slaughter at six months of age. Ruminal contents were collected and assessed to identify rumen bacteria, based on 16S rDNA sequencing analysis. A total of 17 phyla were identified, among which Bacteroidetes, Firmicutes, and Proteobacteria were dominant in both groups. The abundance of Firmicutes was higher in grazing group than in the ration group, while that of Proteobacteria was opposite. Besides the dominant phyla differences, the abundance of Fibrobacteres, Tenericutes, Elusimicrobia, and Cyanobacteria was significantly higher in the grazing group compared with the ration group. At genus level, a total of 174 genera were identified. The abundance of Rikenellaceae_RC9_gut_group, Dialister, Lachnospiraceae_NA, Catonella, Ruminococcaceae_UCG-014, Lachnospiraceae_NK3A20_group, and Fibrobacter in the grazing group was higher than in the ration group. However, the abundance of Succinivibrionaceae_NA was lower in the grazing group, and Succinivibrionaceae_UCG-001 showed a decreasing trend in the grazing group. The two feeding methods may influence the rumen bacterial composition, including the abundance of dominant bacteria, as well as the cellulolytic- and carbohydrate-degrading bacteria in the rumen of Tan sheep.