Activated carbon (AC) was used as an adsorbent for removal of volatile organic compounds (VOCs). The purpose of this research is to study the effect of acidic treatments of activated carbons on toluene adsorption. The physicalchemical properties of activated carbons were characterized by N2 adsorption-desorption isotherms, temperatureprogrammed desorption (TPD). The adsorption amount of toluene showed an order of S-AC-10% > S-AC-5% > A-AC > AC. It was also found that acid solution pH showed a significant influence on adsorption of toluene. Because strong acid treatment increased the surface oxygen group species of activated carbon, and this group was observed to be the carboxyl acid group by TPD analysis. In addition, the toluene adsorption amount by activated carbon increased with the concentration of H2SO4 solution from 5% to 10%. Adsorption ability of activated carbon surface with toluene is thought to increase as the amount of oxygen group on AC increases.