Benzoic acid could be efficiently prepared from aerobic oxidation of toluene using manganese dioxide (MnO2) and N-hydroxyphthalimide (NHPI) as catalysts. The conditions of oxidation, including temperature, amount of catalyst, dioxygen pressure and reaction time, were studied in details. Thus 94.4% conversion of toluene and 98.4% selectivity of benzoic acid could be obtained at 110 degrees C under 0.3 MPa for 3 h in the presence of 10 mol% NHPI and 4 mol% MnO2.