Abstract: Oxidation of toluene catalyzed by N–hydroxyphthalimide (NHPI)/transitions metals with molecular oxygen in the acetic acid reaction medium was reported. The effects of different M(acac)2 (M = Cu，Co，Ni，Fe，Mn) complexes on the oxidation were studied and the results showed that among theses transition metals manganese showed the highest catalytic activity. The effects of different manganese salts were also investigated，and MnCl2 had the highest activity. The reaction conditions of the oxidation process catalyzed by NHPI/ MnCl2 catalyst system were optimized. The optimum conditions were as follows：n(MnCl2)∶n(NHPI)=5×10－2，n(catalyst)∶n(toluene)=10.5%，V(acetic acid)∶V(toluene)= 1∶1，oxygen flow rate 0.05 L/min，reaction temperature 100 ℃ and reaction time 13 h. Under these conditions，61.0% benzoic acid could be obtained with 80.9% selectivity at 75.4% conversion.