The surface of activated carbon was modified by nitric acid (HNO3) and sodium hydroxide (NaOH), and its adsorption capacity to acetylsalicylicSacid(ASP) was investigated. The structural characteristic was represented via Fourier transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM) and the relationship between pore structure and functional groups and adsorption capacity were investigated. It was deduced that the oxygen-containing functional groups were the one which plays a dominant role during adsorption to ASP. The results indicated that both modified activated carbon had a good adsorption capacity to acetylsalicylicSacid. Compared with Freundlich equation, the adsorption process could be better described by Langmuir equation. It was also demonstrated that the adsorption to ASP of activated carbon belongs to monomolecular layer adsorption. The maximum adsorption capacity of modified activated carbon could reach 96.1298 mg/g and the adsorption process was better followed with pseudo-second-order kinetic equation.