Abstract: The soils in maize and tobacco succession cropping fields in northwestern Hunan were sampled to analyze the differences of organic carbon in soil aggregates and their relationship with soil organic carbon and its active components. The results showed that, organic carbon contents in soil aggregates of maize and tobacco succession cropping fields increased with the increase of soil aggregate size. Soil organic carbon was mainly stored in >2 mm aggregates in corn succession cropping field (CSCF) and in >2 mm and 2-0.25 mm aggregates in tobacco succession cropping field (TSCF). Compared to TSCF, the soil aggregates of CSCF had higher organic carbon content, carbon sequestration capacity and contribution rates to soil organic carbon by 0.25-0.053 mm aggregates. In both soils, organic carbon of >2 mm soil aggregates were the most relevant to soil total organic carbon, meanwhile soil labile organic carbon (EOC) and particulate organic carbon (POC) showed significant or extremely significant positive correlation with the contribution rates to soil organic carbon by > 2 mm and 2-0.25 mm aggregates carbon. The results suggested that increasing the proportion of macro-aggregates and their carbon sequestration capacity favor to repair and improve soil quality in CSCF and TSCF in northwestern Hunan.