Abstract: This study investigated the carbon storage and its compositional characteristics of Larix principis-rupprechtii forests across different forest farms in the Ulanqab region, using field sampling and laboratory analysis. The results indicated that the total vegetation biomass in young, middle-aged, near-mature, and mature forests was 67.04 t·hm⁻², 101.06 t·hm⁻², 108.17 t·hm⁻², and 92.37 t·hm⁻², respectively. Tree biomass accounted for the largest proportion of total biomass, ranging from 89% to 94%, with the highest tree biomass observed in near-mature forests at 101.10 t·hm⁻². Vegetation carbon density in these forest age classes was 34.68 t·hm⁻², 53.36 t·hm⁻², 57.42 t·hm⁻², and 44.62 t·hm⁻², respectively. Soil carbon density in the 0-100 cm layer was 84.3 t·hm⁻², 179.5 t·hm⁻², 172.6 t·hm⁻², and 217.4 t·hm⁻² for young, middle-aged, near-mature, and mature forests, respectively. The 0-40 cm soil layer contributed 55.16% to 61.59% of the total soil carbon density in the 0-100 cm profile across all forest age classes. Soil carbon density decreased with increasing soil depth and constituted over 70.85% of the total ecosystem carbon density. No significant differences were observed in shrub-herb or litter carbon density among the forest age classes. Mature forests exhibited the highest ecosystem carbon density (316.02 t·hm⁻²), whereas young forests had the lowest (118.98 t·hm⁻²). Similarly, carbon storage was greatest in mature forests (1.661 MgC) and lowest in young forests (0.065 MgC), with middle-aged and near-mature forests storing 0.568 MgC and 0.517 MgC, respectively. The total carbon stock across the seven state-owned forest farms in Ulanqab City was estimated at 2.81 MgC.