There has been increasing concerns worldwide with the potential of C sequestration of croplands for greenhouse gas emission mitigation under the Kyoto Protocol. China is facing the great pressure under the Kyoto Protocol in reducing the rapid increasing emission of CO2 resulted from the rapid industrialization. China agriculture is meantime facing the double challenge of stabling the food production under the shortage of arable lands with decreasing soil productivity and of enhancing the C sink for mitigating the increasing CO2 emission. This paper deals with the issues of the study on status and dynamics of organic carbon stock, C sequestration potential of agricultural soils of China and the future research need. The general poor storage of organic carbon and the apparent significance in crop productivity in the cropland soils of China offers a great potential and, however, an urgent need for C sequestration agriculture in China. Although there had been a general trend of topsoil C storage reduction before 1980's, different pattern of C dynamics had been reported in the major areas of cropland soils since then. Significant C sequestration trend have been observed in paddy soils, upland croplands in Central and South China, while the organic carbon stock of croplands in Northeast China had been continuously lost for the last 2 decades. While the total soil C sequestration of China could be as high as 11Pg as estimated by Lal (2002), that of cropland soils may reach 5 Pg when the cultivation-induced lose of topsoil SOC stock is expected to retrieve under well performed management practices. Estimated C sequestration rate ranges from 15 Tg/a to 30 Tg/a in the last two decades, the future potential rate may reach 200Tg/a with a socio–economical potential of 40-80 Tg/a in the coming 20-50years under C sequestration agriculture. While the enhancement of SOC in the cropland soils for the last 2 decades could be largely attributed to the increase of organic input due by the crop yield increases, crop residue return, balanced fertilization, crop rotation, reduced tillage and de-intensification had exerted considerable contributions. Enhancement of physical protected but bioactive or labile carbon in soil aggregates may account for the C sequestration in cropland soils. Nowadays a C sequestration strategy as a win-win strategy is well accepted in China agriculture for commitment to the Kyoto Protocol, and the issues for priority researches had arisen as follows: (1) the overall C stock of China cropland soils and the changing dynamics with the agricultural development at various scales; (2) features of C cycling in cropland soils with land fragmentation, and under intensified agriculture and high chemical inputs; (3) coupling mechanisms of soil C sequestration and productivity enhancement for different farming systems for sustainable agriculture in the future. Practical measures for cost-effective C sequestration and the associated pedo-chemical mechanisms would be also the research targets for soil science and agronomy. Implementation of C sequestration agriculture will be a key to China's sustainable agriculture in the early 21th century to meet the commitment to the Kyoto Protocol and buys opportunity for China to compensate the fast increasing CO2 emission due to the rapid industrialization. Key words: Bioactive carbon; C sequestration；China; CO2 mitigation；cropland soils; food security; global change; Kyoto Protocol; physical protection.