The solubility of CO2 in 1-butylpyridinium bis(trifluoromethylsulfonyl)imide C4pyTf2N ionic liquid has been determined using Magnetic Suspension Balance instrument at 298.15 K and in the pressures up to about 27 bar. A group contribution method, namely UNIFAC has been used to fit the experimental data. The interaction parameters of the model were estimated. The predicted CO2 solubility data by the model shows good agreement with the experimental data. © 2012 American Institute of Physics.