Fudan University (FDU)-type mesoporous polymer (FDU-15) was sulfonated by fuming sulfuric acid. The application of FDU-15 and sulfonated FDU-15 (FDU-15-SO3H/t, t = 9 h, 18 h, or 27 h) in removing of U(VI) was explored comprehensively. The adsorbents were characterized by various techniques. The effects of sulfonation time, initial pH values, shaking time, initial concentrations, and temperature on adsorption were optimized. Besides, the desorption and reusability, as well as adsorptive selectivity were investigated. The results indicated high adsorption (43.65 ± 2.11 mg g−1) was achieved under weak acid condition (pH 2.0) for FDU-15-SO3H/9 h. In short, FDU-15-SO3H/9 h may be a superior adsorbent to remove the U(VI) in wastewater. [ABSTRACT FROM AUTHOR]