A novel adsorbent of covalently bounded quaternary ammonium activated carbon (CQA) was prepared by silylation reaction with both organosilicon quaternary ammonium salt (QA) and activated carbon (AC) as raw materials. The CQA was characterized by FTIR, SEM and BET. The results showed that QA was successfully loaded on the surface of AC by covalent binding, and had an important influence on the morphology and structure of AC. The nitrate and phosphate adsorption capacities for CQA were greatly improved. The adsorption behaviors of nitrate and phosphate from aqueous solutions on CQA were investigated using batch experiments. The kinetics study revealed that adsorption of nitrate and phosphate onto CQA followed the pseudo-second-order kinetic model, indicating that the adsorption process was mainly controlled by the chemisorptions. The adsorption data fitted Langmuir and Freundlich isotherm models well, and the maximum nitrate and phosphate adsorption capacities for CQA were 14.829 and 8.442 mg/g, respectively. The effects of pH on the adsorption of nitrate and phosphate were also investigated. The results showed that when pH was from 4 to 9, it was suitable for simultaneous removal of nitrate and phosphate from aqueous solution by CQA.