Abstract: By using balance reaction method, this paper studied the adsorption characteristics and thermodynamic properties of DNA on four kinds of red soil colloids (organic matter-contained coarse clay, organic matterremoved coarse clay, organic matter-contained fine clay, and organic matter-removed fine clay). The DNA adsorption on the four red soil colloids was a process of fast reaction, and the adsorption isotherms were conformed to the Langmuir equation, with the corresponding correlation coefficient (r²) being 0.974, 0.991, 0.958, and 0.975, respectively. The maximum adsorption amount of DNA on the colloidal particles followed the order of organic mattercontained fine clay > organic matterremoved fine clay ＞ organic matter-contained coarse clay ＞ organic matterremoved coarse clay, implying that the size and organic matter content of colloidal particles played an important role in DNA adsorption. Electrolyte concentration and type and adsorption system pH were the main factors affecting the DNA adsorption on the four soil colloids. Within a definite electrolyte concentration range (NaCl < 60 mmol·L^-1 and CaCl2 <10 mmol·L^-1), the adsorption amount of DNA on the red soil colloids increased significantly with the increase of electrolyte concentration. As compared with sodium ion, calcium ion had a greater promotion effect on the DNA adsorption, but the effect decreased significantly with the increase of adsorption system pH. The DNA adsorption on the organic matter-contained red soil colloids was an endothermic reaction, while the DNA adsorption on the organic matter-removed red soil colloids was an exothermic reaction. The DNA adsorption on the red soil colloids was a process of entropy increase.