Two types of predictive thermodynamic models, i.e., the UNIFAC model and GCLF EOS (group contribution lattice fluid equation of state), were applied to predict the solubility of SO2 in ionic liquids (ILs). The group interaction parameters were estimated by correlating the solubility data of SO2 in ILs exhaustively collected from the articles published until July 2015. It was verified that both the UNIFAC model and GCLF EOS could be used for predicting the solubility of SO2 in ILs, but the UNIFAC model gives results that are better than those of GCLF EOS. The UNIFAC model then was used to identify the structure property relation for SO2 solubility and selectivity of CO, to SO2, whereas GCLF EOS was used to investigate the volume expansivity of ILs upon the addition of SO2. The results showed that volume expansivity is independent of the different combinations of cations and anions and exhibits a linear relationship with SO2 solubility in ILs.