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This study was conducted to examine the soil aggregate distributions and their relationship with microbial biomass carbon (C) concentration and soil C in Pinus rigidaand Larix kaempferiplantations. Soil samples of 0–10 cm, 10–20 cm, and 20–30 cm depth were collected and the microbial biomass C concentration was measured. The soils were then classified into four aggregate size classes by wet-sieving procedure [large macroaggregate (>2000 μm), small macroaggregate (250–2000 μm), microaggregate (53–250 μm), and silt-plus-clay (<53 μm)] and the C content of each aggregate size class was analyzed. The L. kaempferiplantation contained more macroaggregate over 250 μm than the P. rigidaplantation did. The mean weight diameter (MWD) of the soil aggregate up to 30 cm depth was 1.26 mm and 1.45 mm in the P. rigidaand L. kaempferiplantations, respectively, and it decreased with soil depth. The microbial biomass C concentration up to 30 cm depth was 510 μg C g soil−1for the P. rigidaplantation and 764μg C g soil−1for the L. kaempferiplantation, and it was greatest in the surface soil in both plantations. The mean soil C concentration up to 30 cm depth was 2.00% for the P. rigidaplantation and 2.88% for the L. kaempferiplantation. In both plantations, the soil C concentration was higher in the surface soil than in the deep soil. However, there was no significant difference of C concentration among the soil aggregate size classes. The soil C content up to 30 cm depth in the P. rigidaand L. kaempferiplantations were 47.69 Mg ha−1and 61.49 Mg ha−1, respectively, and were also higher in the surface soil than in the deep soil. In both plantations, macroaggregate contained more Ccontent than microaggregate did. The microbial biomass C and soil C concentrations were significantly higher (P < 0.05) in the L. kaempferiplantation than in the P. rigidaplantation due to the effect of species difference. The MWD and C content tended to be greater in the L. kaempferiplantation than in the P. rigidaplantation, but the differences were not significant. In this study, the soil aggregate size, microbial biomass C and soil C concentrations were positively correlated with one another.