Amino-functionalized ionic liquids (IL) are often applied to fix CO2. However, as far as we know, none of them have ever been reported to exhibit considerable physical CO2 capture. Herein, we describe an amino-functionalized room-temperature ionic liquid, 1-butyl-3-methylimidazolium 3-amino-1H-1,2,4-triazolate ([Bmim][ATZ]), with an unusual ultrafast physical CO2 capture at room temperature and atmospheric pressure. Within the time needed for a chemisorbent to reach an equilibrium, 15 adsorption and desorption cycles are finished for [Bmim][ATZ], with an accumulative molar ratio of up to 2.04. The CO2/IL ratio for one adsorption process reaches 0.14, which is 4 times the highest recorded physical CO2 solubility by [thtdp][Cl] (trihexyltetradecylphosphonium chloride). The first theoretical study on anion-anion interactions of ionic liquids is reported, which rationalizes the inhibition of chemical adsorption. These results provide a new perspective on the aspect of CO2 capture, as well as designing of ionic liquids.