Carbon adsorbents were chemically modified to have base sites on their surfaces, and the adsorption characteristics of carbon dioxide on them were investigated. Three kinds of carbon materials were used as support materials : two activated carbons and a carbon black. Base sites were introduced by impregnating the support materials with calcium acetate solution, followed by calcination at 700 degrees C for 2 hours in an inert gas flow. Chemical modification reduced the surface areas of adsorbents due to the blocking of micropores. Irreversible adsorption of carbon dioxide occurs up to 300 degrees C due to chemisorption. However, reversible adsorption was possible by pretreating adsorbents with carbon dioxide. Strong interaction between carbon dioxide and base sites enhanced adsorption of carbon dioxide at higher temperatures up to 250 degrees C.