The ionic liquid 1-methyl-3-(3-sulfopropyl)imidazolium chloride ([MIMPs]Cl) as a catalyst demonstrates high efficiency in the one-pot aerobic oxidative condensation of arylmethylamines with 1,2-phenylenediamines to give benzimidazoles. The products were characterized by 1H NMR. First, the condensation of benzylamine with o-phenylenediamine to give 2-phenylbenzimidazole was used as a model reaction to screen the catalysts and optimize the reaction conditions, which were found to be [MIMPs]Cl with 25 mol% of basic substrate as catalyst, oxygen of 0.1 MPa as oxidant, dimethylformamide (DMF) as solvent, benzylamine to o-phenylenediamine molar ratio of 2.5:1, reaction temperature of 100 ℃, and reaction time of 20 h. Under the optimal conditions, the yield of 2-phenylbenzimidazole reached 92%. Then, the method was applied to other substituted substrates and good to excellent results were obtained, indicating its broad substrate tolerance. This strategy is benign to the environment and suitable for the synthesis of pharmaceutical intermediates due to its advantage of using molecular oxygen as the oxidant under metal-free conditions.