A series of new ionic liquids were prepared by neutralizing five different imidazole derivatives with two imide-type acids such as bis(trifluoromethanesulfonyl)imide and bis(perfluoroethylsulfonyl)imide, and their ionic conductivity and thermal properties were investigated. All the imidazolium salts synthesized are liquid at room temperature. The ionic liquid of the methylimidazolium bis(trifluoromethanesulfonyl)imide system has the best ionic conductivity, 7.23 x 10(-3) S cm(-1) at 25 degreesC, of the series of five imidazolium salts.