Novel azolate-type ionic liquids (ILs), alkyltributylphosphonium benzimidazolates (alkyl chain: methyl, butyl, and octyl), were prepared by neutralization of the corresponding alkyltributylphosphonium hydroxides with benzimidazole. All the azolate-type ILs prepared here showed high ionic conductivities above 10(-3) S cm(-1) at 80 degrees C, and good thermal stability over 300 degrees C. They are expected to be useful platforms for functional lLs having good thermal stabilities.