We found that stereoregular isotactic poly(methyl methacrylate) (it-PMMA) (mm = 97%) and syndiotactic poly(methyl methacrylate) (st-PMMA) (rr = 90%) with a narrow molecular weight distribution form a stereocomplex in ionic liquids such as 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6). The stereocomplex formation brought about the gelation of BMIPF6 and was fully thermoreversible accompanied by a sol-gel transition at around the melting point of the crystalline stereocomplex in BMIPF6 as evidenced by differential scanning calorimetry and polarized optical microscopy measurements of the gel. The effects of ionic liquids, the molar ratio of the it- and st-PMMAs, and the heating and cooling rates on the stereocomplex formation accompanied by gelation were also investigated. The fully thermoreversible gel in the ionic liquid with a high melting point (T-m = 175.0 degrees C) due to the unique stereocomplex formation may provide a new opportunity to fabricate advanced electrochemical devices.