Abstract: Two amidoxime-functionalized mesoporous silica (SBA-15) materials were prepared by a post-grafting method, and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunner Emmet Teller (BET) measurements, and elemental analysis. The sorption of U(Ⅵ) on SBA-15 and amidoxime-functionalized SBA-15 was investigated by a batch method. The results indicate that the pore structure of amidoxime-functionalized mesoporous silica is the same as SBA-15, but the pore volume and BET surface area decreases. Compared to SBA-15, the sorption ability of amidoxime-functionalized SBA-15 for U(Ⅵ) is obviously increased. SBA-15-2AO with more amidoxime groups has the highest adsorption capacity of about 0.885 mmol/g for U(Ⅵ), which is 4 times of SBA-15. The sorption process is exothermic and follows a pseudo-second-order type sorption kinetics for all materials. In addition, U(Ⅵ) adsorption depends strongly on pH, but the effect of ionic strength is weak. Amidoxime-functionalized mesoporous silica exhibites high selectivity and a better sorption ability for U(Ⅵ) over a series of competing metal ions.