The distribution of soil aggregates and the storage of organic carbon (C ) are important parameters to evaluate of physical and chemical properties of soil. This study was carried out to aim at (i) assessing the ratios of different soil aggregates in the studied soils, (ii) investigating the distribution of organic C and the fractions of soil easily degradable organic C present in different soil aggregates and (iii) elucidating the role of soil aggregates in protecting soil organic C against microbial degradation. The study was done by separating soil aggregates (macro-aggregate, aggregate, micro-aggregate and silt-clay) through wet sieving fractionation procedure, analyzing the total contents of organic carbon presenting in different levels of soil aggregate and assessing the fractions of easily degradable organic C based on measuring the evolution of CO₂-C through C mineralization. The total amounts of organic C present in different levels of soil aggregate were evaluated to reveal the role of soil aggregates in protecting organic C from soil microbial degradation. Soils were sampled from soil groups of Arenosols, Ferralsols and Gleysols located in Southern Vietnam and were under different cropping systems. Arenosols, Ferralsols soils were cultivated with black peper, whereas Gleysols soil was under rotation system of vegetables. The results showed that soils Arenosols and Ferralsols contain high proportion of aggregate (53 àm ? 0.3 mm) and silt-clay (

Keywords: soil aggregate, easily degradable organic C, Arenosols, Ferralsols, Gleysols