In this study, to improve oxidative degradation of aqueous phenol, an advanced oxidation process of UV/H₂O₂ was combined with microwave irradiation. This new process, comparing with a conventional UV/H₂O₂ process, was found to considerably accelerate the oxidative degradation rate. For example, it accelerates up to 50 % increase of the reaction rate and more than 60 % increase of the removal efficiency based on TOC values, without any thermal effect. In the course of the oxidative degradation of aqueous phenol, several kinds of intermediates, such as hydroquinone, catechol, maleic acid, glyoxalic acid, formic acid, and etc., could be observed by HPLC analyzer. Benzene ring intermediates such as hydroquinone and catechol were both formed and degraded much more rapidly in the UV/H₂O₂ process with microwave irradiation system than in the conventional process. High efficiency of the new process with microwave irradiation will arise probably from such facts that, since microwave violently vibrate polar substances, reactant molecules might change into high excited states to be easily oxidized and such vibration of polar substances can also improve the mass transfer rates between reactants.