A strategy to prepare liquid anion-functionalized pillar[5]arene by incorporating a large asymmetrical cation on the rims was proposed. This kind of pillar[5]arene-based ionic liquid showed high thermal stability, good CO2 absorption capacity, and excellent reversibility. In contrast with the neutral pillar[5]arene and the noncyclic monomeric analogue, pillar[5]arene-based ionic liquid exhibited significantly enhanced CO2 absorption capacity. Through a combination of absorption experiments, spectroscopic investigations, and quantum chemical calculations, the results indicated that the increased capacity originated from multiple-site interactions between CO2 and the carboxylic anion, which was enhanced by the cavity of pillar[5]arene. This work provided an efficient methodology for preparing a liquid macrocyclic host as well as improving gas absorption.