In this study, effects of humic acid(HA) on the dispersion of soil (red soil and yellow-brown soil) and clay minerals (kaolinite and montmorillonite) were investigated. The results showed that HA played an importmant role in dispersion of soil and clay minerals. The removal of soil organic matter with H₂O₂ obviously decreased the clay dispersion, whereas the addition of HA led to a great increase in the clay dispersion. The dispersion of Na-kaolinite clay was very week, but that of Na-montmorillonite clay was very strong, which were related to the resources and amounts of the charges. On the other hand, with the addition of HA, the dispersion of Na-kaolinite clay was improved abruptly, but that of Na monttnorillonite clay changed little. The results Further indicated that HA effect on clay dispersion was affected by the mineral types.