As shown in a previous study, soil carbon sequestration of the three typical paddy soils, i.e. Cabhaplic, Acihaplic and Typfec Stagnichydroagric Anthrosols in South China was related to physical protection in microaggregate size fractions, though varying with the soil types and management practices. Herewith the authors report a study on analysis of SOC binding forms in size fractions of micro-aggregates obtained by low-energy ultrasonic dispersion procedure from the studied types of paddy soils. Calcium bound SOC (Ca-SOC) was predominant in the coarse fraction of 2 000~200 μm, with the highest and the lowest content in purple paddy soil and in red paddy soil, respectively. On contrast, iron/aluminum oxyhydratesbound SOC(Fe(Al)-SOC) dominated the size fraction of <2 μm, with the highest and the lowest content in red paddy soil and in purple paddy soil, separately, which was in coincidence with the content distribution of Fe/Al oxyhydrates in various particle size fractions. Statistic analysis indicated significant positive correlation of ratio of LOC to SOC with that of Ca-SOC to SOC, and significant negative correlation of the ratio of LOC to SOC with that of Fe (Al)-SOC to SOC. Ca-SOC and Fe(Al)-SOC in coarse aggregates of 2 000~200 μm showed the most sensitive response to longterm tillage and fertilization practices, and SOC accumulation in paddy soils under good management practices was represented mostly as increase in Fe(Al)-SOC. Fe/Al oxyhydrates in coarse aggregates from the red paddy soil among the three showed the most intensive chemical protection of organic carbon. Thus, chemical protection of SOC physically protected in coarse fractions by binding with Fe/Al oxyhydrates during micro-aggregate turnover was supposed to be a prevailing mechanism of SOC sequestration in these paddy soils.