Adsorption and desorption of salmon sperm DNA on four different colloidal fractions from Brown Soil and clay minerals were studied.The adsorption isotherms of DNA on the examined soil colloids and minerals conformed to the Langmuir equation. The amount of DNAadsorbed followed the order: montmorillonite[fine inorganic clayOfine organic clayOkaoliniteOcoarse inorganic clayOcoarse organicclay. A marked decrease in the adsorption of DNA on organic clays and montmorillonite was observed with the increase of pH from 2.0 to5.0. Negligible DNA was adsorbed by organic clays above pH 5.0. As for inorganic clays and kaolinite, a slow decrease in DNA adsorptionwas found with increasing pH from 2.0 to 9.0. The results implied that electrostatic interactions played a more important role in DNAadsorption on organic clays and montmorillonite. Magnesium ion was more efficient than sodium ion in promoting DNA adsorption on soilcolloids and minerals. DNA molecules on soil colloids and minerals were desorbed by sequential washing with 10 mM Tris, 100 mM NaCland 100 mM phosphate at pH 7.0. A percentage of 53.7–64.4% of adsorbed DNA on organic clays and montmorillonite was released, whileonly 10.7–15.2% of DNA on inorganic clays and kaolinite was desorbed by Tris and NaCl. The percent desorption of DNA from inorganicclays, organic clays, montmorillonite and kaolinite by phosphate was 39.7–42.2, 23.6–28.8, 29.7 and 11.4%, respectively. Data from thiswork indicated that fine clays dominate the amount of DNA adsorption and coarse clays play a more important role in the binding affinity ofDNA in soil. Organic matter may not favor DNA adsorption in permanent-charge soil. The information obtained is of fundamentalsignificance for the understanding of the ultimate fate of extracellular DNA in soil.