Fractions of organic carbon in upland soils different in fertilization were determined with a physical fractionation technique, and samples of the soils were incubated in lab to observe dynamics of mineralization of organic carbon in the soil. Calculation of the biologically active organic carbon pool was fitted with a first-order kinetic model. Results indicated that in soils different in fertilization, the content of organic carbon in light fraction (LF-C), coarse intra-aggregate particulate organic matter (iPOMc-C), fine intra-aggregate particulate organic matter (iPOMf-C) and mineral associated organic carbon (mSOC) accounted for 7%~10%, 0.5%~1.5%, 4%~7% and 76%~85%, respectively, of the total organic carbon (TOC) in soils, and was significantly correlated with TOC. Barnyard manure (manure+NPK) increased the contents of carbon in all fractions, more significantly than green manure (green manure+NPK) and CK (NPK). The dynamic of soil organic carbon mineralization under incubation consisted with the first-order kinetic model. Both green manure and barnyard manure significantly increased the size of biologically active organic carbon pool (C₀), and the latter showed a better effect, than the former, but had a lower turnover rate (k). The contents of organic carbon in all fractions were significantly related to C₀ at the 0.01 level, and so were the percentages of all the fractions to TOC, except LF-C.