Four different forest lands were chosen in the hill region of central Hunan, China. They were:Loropetalum chinense-Vaccinium bracteatum.-Rhododendron mariesii scrub-grass-land (LVR), L. chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-L. chinense coniferous-broad leaved mixed forest (PLL) and L. glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG). In order to elucidate the effects of forest degradation on soil organic carbon, the soil partical-size fractionation method was adopted to study the changes of soil organic carbon (SOC) concentrations and their distributions in different particle-size fractions in the mid-subtropical zone of China. The result showed that the percentage of > 2 μm particles (sand, silt) increased, while that of < 2 μm clay particles decreased, and soil texture was coarse sand with the degradation of forest land. SOC concentration had the negative exponential function decreasing trend with the degradation of forest land. SOC pool was mainly composed of silt-C and clay-C in LAG, while those were dominated by silt-C and sand-C in PLL, LCQ and LVR. With the degradation of forest land, Concentrations of SOC in three partical-sized fractions were decline, the distribution proportion of sand-C concentrations increased obviously, but that of clay-C decreased obviously, and the ratio of POC/MOC increased, the SOC fixation, protective effect, stability decreased in the same layer. The changes of community species composition, biomass and soil particles composition with the degradation of forest land were the main factors leading to the decrease of SOC contents and stability of forestlands.