The low-pressure isothermal sorption Of CO2 in poly(ionic liquid)s (PILs) with varied structures including different cations, anions, backbones, and substituents was investigated to probe structure effects on the CO2 sorption. An ammonium cation with short alkyl group, BF4 anion, and polystyrene backbone was found to favor CO2 sorption in PILs. CO2 sorption in the PILs fitted the dual-mode model very well, suggesting that the CO2 sorption consists of dissolution in the polymer matrix and Langmuir sorption in the microvoids.