Given the fact that the basicity of imidazolate was higher than that of acetate, imidazolate-based ionic liquids (ILs) were developed to be studied. By combining six different cations, including traditional cation, functionalized cation, and dication, together with imidazolate, a series of ILs were prepared and found to be effective for CO2 capture. The mechanism of the studied ILs was proposed as the formation of the carboxylation reactions on C2 position of the imidazolium rings. A strong interaction between the newly formed carboxylate portion of the zwitterion and the C2-H proton of another cation was also formed, leading to a 0.5 molar ratios of CO2 to IL. In addition, the CO2 absorption capacity of dicationic IL was 1.0 molar ratio, twice that of the monocationic analogue. Significantly, an improvement on absorption result was exhibited by the amino-functionalized IL, but similar performance was not observed in the hydroxyl-functionalized one. The effects of operating pressure and temperature on CO2 absorption were also discussed.