Soil organic carbon (SOC) was considered to be a key index in evaluation of soil degradation and soil C sequestration.To discuss the spatial-temporal dynamics of SOC in arable layer in reversed desertification area,a case study was conducted in Yulin City,Shaanxi Province,China.Data of SOC were based on general soil survey in 1982 and repeated soil sampling in 2003.Soil organic carbon content (SOCC) was determined by K2Cr3O7-FeSO4titration method,and soil organic carbon density (SOCD) was calculated by arithmetic average and area weighted average method,respectively.On average,SOCC and SOCD of the arable layer in the study area from 1982 to 2003had increased 0.5 lg/kg and 0.16kg/m2,respectively.Considering main soil types,the widest distributed Arid-Sandic Entisols had lowest values and increments of SOCC and SOCD during the study period;while the second widest Los-Orthic Entisols had higher values and increments of SOCC and SOCD,compared to the mean values of the whole region.The results indicated that reversed desertification process was due to the modification of land use and management practices,such as natural vegetation recovery,planting grass,turning arable land to grassland,and soil and water conservation etc.,which can improve SOCC and SOCD and thus enhance soil C sequestration.