Abstract: By static adsorption experiments, the effects of pH, ionic strength, adsorption time, uranium initial concentration, adsorbent dosage, red soil-colloid size, and organic matters on the biosorption capacity of red soil-colloid extracted from the soil around uranium tailing for uranium were studied. The adsorption process was analyzed by thermodynamics and kinetics, and the adsorption mechanism was characterized by the element analysis,infrared spectroscopy and scanning electron microscopy. The results show that the adsorption capacity for U(Ⅵ) on red soil-colloid increases with the decrease of ionic strength or particle size, increases with the initial concentration of uranium, decreases with the increase of the amount of red soil-colloid; the saturated adsorption capacity max can be up to 76.76 μg/mg by red soil-colloid which diameter is less than 1 μm at 25 ℃ and pH＝3.5, when the ionic strength is 0.001 mol/L. FT-IR micrograph before and after red soil-colloid adsorbed uranyl ions indicates that the red soil-colloid are mainly composed of hydroxyl, carbonyl, Si—O, Si—O—Fe, etc. The adsorption of U(Ⅵ) on red soil-colloid follows Langmuir adsorption isotherm, and the pseudo-second-order equation provides the best correlation for the adsorption process.