Three groups of micro-aggregate, including water dispersed (G₀,sodium dispersed (G₁) and mechanical-sodium dispersed micro-aggregate (G₂),were separated by the peptization method from three groups of paddy soil derived from Quarternary red clay. The total amounts of micro-aggregates are 54, 58, 60% based on air-dry soil and the ratio of G₀+G₁:G₂ are 0.45, 0.94, 1.46 respectively.