Ammonium adsorption and desorption were investigated with colloid samples of black soil,manured loessial soil, yellow brown earth, red earth and latosol as well as clay minerals. Adsorption of ammonium by soil colloids and clay minerals fitted to the two surface Langmuir adsorption equation. Binding strength was in the order: yellow brown earth > black soil,manured loessial soil>red earth>latosol, but the ammonium desorption ratio showed the opposite sequence. Langmuir parameter (K₁) was directly proportional to the relative affinity of soil colloids for ammonium (A). Langmuir equation constant (M₁+M₂) was positively correlated with CEC of samples, while the difference between K₁ before and after removing organic matter (ΔK₁) was negatively correlated with ΔOM.Removing organic matter could increase the affinity of soil colloids for ammonium and tended to decrease the ammonium desorption ratio.Annnonium adsorption behavior was determinedby the composition and surface properties of soil colloids, it was also influenced by clay-humus intereaction. Adsorption sites with permanent negarive charge showed stronger selectivity for ammonium than those sites with variable charge.