The reaction activities of ZSM - 5 and 7 - A12O3 for disproportionation of toluene under supercritical conditions was investigated. The experiments for 7 - A12O3 disclosed that coke deposition on the catalyst was inhibited and the activity of 7 - A12O3 was maintained constant under the supercritical conditions. The results of the runs on ZSM - 5 indicated that coke formation could not be prevented and thus the activity could not be maintained under supercritical conditions. The mechanism of prevention of coke formation was discussed.