Abstract: Fencing (enclosure) is one of the strategies used to promote the natural restoration of ecological communities on the desert steppe in Ningxia. To explore the effects of enclosure on soil organic carbon and its distribution, field studies were conducted at sites with 3, 5, 7, and 10 years of enclosure. Soil samples were collected to determine the total organic carbon concentration and its distribution at different soil depths and in soil aggregates. The results showed that the soil organic carbon concentrations were higher in 7-year and 10-year enclosed grasslands than in those enclosed for shorter times, except at 0-5 cm depth. The concentrations of soil organic carbon were lower in the 0-5 cm and 5-10 cm soil layers than in the 10-20 cm and 20-40 cm soil layers. The soil organic carbon concentrations in soil aggregate particles at 0-10 cm depth were highest in the 3-year enclosed grassland, while those at 10-40 cm depth increased with longer enclosure times. The maximum soil organic carbon contents were in aggregates with 1-0.5 mm and 0.5-0.25 mm diameters. Aggregates of <0.25 mm, >5 mm or <0.25 mm, and >5 mm made the largest contributions to soil organic carbon content at 0-10 cm depth, 10-20 cm depth and 20-40 cm depth, respectively. The contribution of aggregates to soil organic carbon content decreased with increasing enclosure times. As the soil depth increased, the contribution of aggregates to soil organic carbon content decreased, but the contributions of macroaggregates to soil organic carbon content increased. In conclusion, enclosure was beneficial for carbon sequestration. The restoration of the ecosystem on the degraded desert steppe appeared to undergo a transition at the 7th year of enclosure.