An assessment of organic matter and carbon stocks in the woody vegetation of a eutrophic fen in the middle taiga of the Komi Republic is presented. Woody vegetation is represented by 8 plant species, including 5 shrubs. Four vegetation communities have been identified in the forested sites of the fen. The aboveground biomass of woody plants was estimated from 25 model trees, and the underground biomass was estimated using the soil monolith method. The biomass of woody plants in the fen varied from 120 to 3871 g/m2, with the bulk (70–74 %) of organic matter accumulating in the aboveground organs. The tree layer biomass stock is shown to depend on the type of community, the number and qualities of the trees. Birch and pine trees < 4 cm in diameter contribute the most to organic matter acumulation. Birch-sedgebuckbean communities are characterized by the highest organic matter stock, while birch-sedge-buckbean moss communities have a lower stock. The tree-layer biomass of sparsely treed communities is 9–32 times lower than in forested areas of the fen. It is estimated that, depending on the type of community and abundance, woody plants accumulate 56 to 1742 g C/m². It was found that the woody plants in the fen area with the densest tree stand accumulate an average of 969 g C/m². Birch accounts for 64 to 73 %, and pine for 12 to 31 % of the carbon stocks of woody vegetation in the fen. Stem wood contains about a half of the carbon stock. These results can be used to estimate the total organic matter stores and the carbon cycle in the ecosystem of a eutrophic fen.