The solubility of carbon dioxide in room temperature ionic liquids (RTILs), dialkylimidazolium dialkylphosphates, was measured at 313–333 K and at pressures close to atmospheric pressure, from which Henry's law coefficients, standard Gibbs free energy, enthalpy, and entropy changes of solvation were derived. The CO 2 solubility in the dialkylimidazolium dialkylphosphate was found to increase with increasing chain length of the alkyl groups on the cation and/or the anion as was similarly found in other RTILs. Among various dialkylimidazolium dialkylphosphates tested, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][Et 2 PO 4 ]) and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][Bu 2 PO 4 ]) exhibited the comparable or better capability of dissolving CO 2 in comparison with that of [BMIM][BF 4 ], but their absorption capacities were still lower than that of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf 2 N]).