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Afforestation is conducive to soil carbon (C) sequestration in semi-arid regions. However, little is known about the effects of afforestation on sequestrations of total and labile soil organic carbon (SOC) fractions in semi-arid sandy lands. In the present study, we examined the effects of Caragana microphyllaLam. plantations with different ages (12- and 25-year-old) on sequestrations of total SOC as well as labile SOC fractions such as light fraction organic carbon (LFOC) and microbial biomass carbon (MBC). The analyzed samples were taken from soil depths of 0–5 and 5–15 cm under two shrub-related scenarios: under shrubs and between shrubs with moving sand dunes as control sites in the Horqin Sandy Land of northern China. The results showed that the concentrations and storages of total SOC at soil depths of 0–5 and 5–15 cm were higher in 12- and 25-year-old C. microphyllaplantations than in moving sand dunes (i.e., control sites), with the highest value observed under shrubs in 25-year-old C. microphyllaplantations. Furthermore, the concentrations and storages of LFOC and MBC showed similar patterns with those of total SOC at the same soil depth. The 12-year-old C. microphyllaplantations had higher percentages of LFOC concentration to SOC concentration and MBC concentration to SOC concentration than the 25-year-old C. microphyllaplantations and moving sand dunes at both soil depths. A significant positive correlation existed among SOC, LFOC, and MBC, implying that restoring the total and labile SOC fractions is possible by afforestation with C. microphyllashrubs in the Horqin Sandy Land. At soil depth of 0–15 cm, the accumulation rate of total SOC under shrubs was higher in young C. microphyllaplantations (18.53 g C/(m2•a); 0–12 years) than in old C. microphyllaplantations (16.24 g C/(m2•a); 12–25 years), and the accumulation rates of LFOC and MBC under shrubs and between shrubs were also higher in young C. microphyllaplantations than in old C. microphyllaplantations. It can be concluded that the establishment of C. microphyllain the Horqin Sandy Land may be a good mitigation strategy for SOC sequestration in the surface soils.