In this work, the solubility of CO2 in sulfonate ionic liquids (ILs), such as trihexyl (tetradecyl) phosphonium dodecylbenzenesulfonates ([P-6,P-6,P-6,P-14][C12H25PhSO3]) and trihexyl (tetradecyl) phosphonium mesylate ([P-6,P-6,P-6,P-14] [MeSO3]), was determined at temperatures ranging from (305 to 325) K and pressures ranging from (4 to 9) MPa. It was found that the difference of the solubility of CO2 in two kinds of sulfonate ILs is not dramatic on the basis of molality. The solubility Of CO2 in [P-6,P-6,P-6,P-14] [MeSO3] is higher than that in [P-6,P-6,P-6,P-14] [C12H25PhSO3]. The solubility data were correlated by means of the extended Henry's law, and the thermodynamic functions, such as the standard enthalpy, standard Gibbs free energy, and standard entropy, were obtained. The Henry's law constant for CO2 in all the investigated ionic liquids increases with increasing temperature.