The contribution of the heterogeneous component of the total conversion of m-xylene to the process of its heterogeneous catalytic liquid-phase oxidation has been studied, as this contribution is most clearly manifested in the case of microwave treatment. It has been shown that microwave irradiation shortens the induction period of the reaction taken to reach a steady state. It has been suggested that the observed increase in the generation rate of free m-xylyl radicals by microwave treatment is due to the appearance at the hydrocarbons/catalyst interface of local overheating regions whose temperature can exceed the weight-average temperature in the reaction space.