Branched polyimide was synthesized by in situ polycondensation of 4,4'-oxydianiline, pyromellitic dianhydride, and 1,3,5-tri(4-aminophenyl)benzene in ionic liquid/zwitterion mixture. Compatibility between network and ionic liquids is important to keep gel shape and ionic conductivity. Only 6.0 wt % of polyimide was enough to keep gel state without phase separation or leakage. The obtained polyimide gel showed excellent thermal stability with decomposition temperature of above 300 degrees C, low glass-transition temperature, and stable ion conduction in a wide temperature range.