Two types of de-ashed (DA) activated carbon were prepared by oxidation (DAOx) and outgassing (DAOxOG) treatment to introduce and reduce surface acidic functional groups. Adsorption of 11 kinds of aromatic compounds on DAOx and DAOxOG was examined experimentally, and adsorption isotherms were obtained for each adsorbate. The adsorption/desorption kinetics of two adsorbates, nitrobenzene and phenol, were further examined to clarify the adsorption mechanisms. The results showed that DAOxOG adsorbed higher amounts of all 11 aromatic compounds than DAOx over the range of concentration tested. Also, the adsorptive behavior on DAOx and DAOxOG differed for each adsorbate. For nitrobenzene, the amount adsorbed on DAOx increased with the increase in the concentration, and the maximum amount was close to that adsorbed on DAOxOG. These trends were not found in the case of phenol. Nitrobenzene and phenol also showed different adsorption and desorption rates on DAOx. These results suggest that the difference in adsorptive behavior of adsorbates on the two types of activated carbons is due to the different adsorptive form of adsorbates caused by the different polar characteristics of their substituent groups.