Highly porous activated carbon is used in the removal of volatile organic compounds (VOCs) and purification of room air. Despite it's wide applications there are relatively few studies on the activated carbon adsorption of VOCs at trace concentrations of ppb levels. Adsorption equilibria were measured by the headspace gas chromatography (HSGC) method using gas chromatography or gas chromatography-mass spectrometer. The reliability of this method was confirmed by comparing the adsorption isotherms of methanol from the volumetric method. Isotherms for three types of activated carbon and six VOCs over a wide range of concentrations were determined and correlated by the Toth and Dubinin-Radushkevich equations, which are generally used for heterogeneous adsorbents such as activated carbon. Furthermore an applying this method to binary adsorption equilibria (dichloromethane + trichloroethylene), the results agreed with values calculated from the Ideal Adsorbed Solution Theory (IAST). It was shown that the adsorption equilibria of low concentration VOCs and multi-component adsorbates could be determined easily and accurately using HSGC method.