Amylose and a dextran of MW 2 million were adsorbed by montmorillonite. However, two dextrans of lower MW did not adsorb on montmorillonite. It is suggested that entropy changes arising from changes in configuration of the macromolecules and the association of water molecules with clay and polymer control the adsorption behavior of uncharged polysaccharides. Poly (galacturonic acid) was adsorbed by aluminum montmorillonite but showed negative adsorption on sodium montmorillonite. The uronic acid components of a soil polysaccharide were adsorbed by montmorillonite if aluminum ions or hydroxy aluminum species were present on the clay; neutral sugar components were adsorbed irrespective of the exchangeable cations present or the pH.