Based on a 26-year-long fertilization experiment in paddy field, effects of fertilization on distribution, density and mineralization of organic carbon in soil profiles in paddy field were studied. Results show: 1) Long-term fertilization significantly increased organic carbon content in the top soil, and Treatments MR (application of organic manure plus return of crop straws) demonstrated a more contributive effect than Treatments CF (application of chemical fertilization alone) on organic carbon accumulation in the top soil. Organic carbon content in the 10~30 cm soil layers of Treatments CF and in the 20~40 cm soil layers of Treatments OM (organic manure) was relatively stable. 2) In the 0~25 cm and 0~50 cm soil layers, organic carbon density was found higher in Treatments OM than in Treatments CF, the highest in Treatments MNP and CNPK, and in Treatment CRN than in Treatment MRN. Compared with CK, Treatment C0 (no fertilization), all the other treatments varied more greatly in organic carbon in the 0~25 cm and 25~50 cm soil layers, Treatments OM did more than Treatments CF, and Treatments CNP and MNPK the most. 3) Organic carbon mineralization reached the peak in the first 2~4 days, and gradually leveled off in the 3 weeks that followed. The rate was higher in Treatments OM than in Treatments CF, with average mineralization rates varying in the range of CO₂ 55.36~75.46 ml kg^-1 d^-1 and stable mineralization rates in the range of CO₂ 10~20 ml kg^-1 d^-1. In the eight weeks of incubation, Treatments OM were always higher than Treatments CF in cumulative mineralization and Treatment MRN was the highest. The total mineralization intensity and stable mineralization rate remained stable in all the treatments.