Thermoreversible gelation of ionic liquids (lLs) was demonstrated using a well-defined ABA triblock copolymer. The ABA triblock copolymer consisted of poly(phenylethyl methacrylate) terminal A blocks and a poly(methyl methacrylate) middle B block. Temperature-tunable thermosensitive sol-gel transition, i.e., low-temperature-sol high-temperature-gel, can be realized because of the lower critical solution temperature aggregation behavior of the A blocks. The sol gel transition behavior of polymer-IL composites can be precisely controlled not only by changing the chemical structure of the A blocks but also by changing that of the ILs.