Mesoporous carbon CMK-3 was synthesized via a hard template method. The structures of the pores were characterized by N-2 adsorption at 77K, XRD, and TEM examinations. The BET surface area and total pore volume were 1115 m(2)/g and 1.11 cm(3)/g, respectively. Adsorption isotherms of carbon dioxide on the CMK-3 in the presence of water were collected. At 275 K and 3.6 MPa, the CO2 sorption capacity was 42 mmol/g with a water to dry carbon weight ratio (R-w) of 2.35. This is 2.26 times as high as that for the dry CMK-3 sample and 23% higher than the highest CO2 sorption previously obtained on activated carbon with preadsorbed water. The enthalpy change obtained from the sorption isotherms was -55.6 kJ/mol, which is lower than the enthalpy for the formation of CO2 hydrate in pure water.