Abstract: Commercial multi-walled carbon nanotubes(MWNTs) were of purified and carboxylated, and characterized by thermogravimetric analysis(TGA) and infrared spectroscopy(IR). The two nanomaterials were applied for the adsorption of uranium ion. The effects of acidity, temperature, time, and uranium initial mass concentration of the solution on the adsorption capacity were studied. The results show the grafted carboxyl group account for 10% of the carboxylated MWNTs mass, and the specific surface of carboxylic MWNTs is higher than the purified MWNTs, and the characteristic absorption peak ν_asyn(1 641cm^-1) of the carboxyl group is observed in the latter IR spectrum. In the pH value range of 3.0-6.0, the adsorption capacity of uranium on the two materials increases with the increase of the pH and equilibrium concentration, and is little influenced by reaction time and temperature. The adsorption isotherm and thermodynamic model of two materials were investigated. The results show that the adsorption can be described by with Freundlich and Langmuir equation, and the largest theoretic adsorption capacity are 47.81 mg/g and 89.09 mg/g, respectively.