The dynamic of interaction among soil aggregates, nutrients and carbon stability following afforestation is not fully understood. The slope position effect on this process is often neglected, but may dominate the topsoil properties due to serious erosion in red soil hilly region of southern China. Two 19-year old Masson pine (Pinus ,massoniana) forest plantations and their neighboring secondary shrubs were selected to study nutrients and carbon stocks in soils and at ecosystem level using excavating, harvesting and modeling methods, and carbon stability in various aggregates and bulk soil using dry sieving and closed-jars alkali-absorption methods. The afforestation did not alter soil C and P stocks. and decreased N stock at 0-75 cm depth, but increased ecosystem C, N and P stocks from 53, 11.6, 1.51 t ha-l to 111, 12.1 1.90 t ha.l, respectively due to tree biomass accumulation. The organic C mineralization potential was much lower in larger aggregates than in smaller aggregates, thus aggregate formation was helpful to improve soil organic C stability, which preferably explained the slope position effect with higher mean weight diameter of aggregates and organic C stability at lower and middle positions than upper position in forest plantations. The shift from shrubs to forests increased organic C stability in various aggregates and bulk soils, which was closely related with the decrease in soil N concentration. and was also influenced by soil bulk density, aggregate components. C/N and N/P ratios. Additionally, slope position significantly affected all variables measured in this study, thus the further research needs pay attention to physical erosion and deposition process when exploring afforestion effect on soil biogeochemistry cycling in the red soil hilly region.